4&#39;-substituted nucleoside reverse transcriptase inhibitors

ABSTRACT

The present invention is directed to 4′-substituted nucleoside derivatives of Formula I 
     
       
         
         
             
             
         
       
     
     and their use in the inhibition of HIV reverse transcriptase, the prophylaxis of infection by HIV, the treatment of infection by HIV, and the prophylaxis, treatment, and delay in the onset or progression of AIDS and/or ARC.

BACKGROUND OF THE INVENTION

The retrovirus designated human immunodeficiency virus (HIV),particularly the strains known as HIV type-1 (HIV-1) and type-2 (HIV-2),have been etiologically linked to the immunosuppressive disease known asacquired immunodeficiency syndrome (AIDS). HIV seropositive individualsare initially asymptomatic but typically develop AIDS related complex(ARC) followed by AIDS. Affected individuals exhibit severeimmunosuppression which makes them highly susceptible to debilitatingand ultimately fatal opportunistic infections. Replication of HIV by ahost cell requires integration of the viral genome into the host cell'sDNA. Since HIV is a retrovirus, the HIV replication cycle requirestranscription of the viral RNA genome into DNA via an enzyme known asreverse transcriptase (RT).

Reverse transcriptase has three known enzymatic functions: The enzymeacts as an RNA-dependent DNA polymerase, as a ribonuclease, and as aDNA-dependent DNA polymerase. In its role as an RNA-dependent DNApolymerase, RT transcribes a single-stranded DNA copy of the viral RNA.As a ribonuclease, RT destroys the original viral RNA and frees the DNAjust produced from the original RNA. And as a DNA-dependent DNApolymerase, RT makes a second, complementary DNA strand using the firstDNA strand as a template. The two strands form double-stranded DNA,which is integrated into the host cell's genome by the integrase enzyme.

It is known that compounds that inhibit enzymatic functions of HIV RTwill inhibit HIV replication in infected cells. These compounds areuseful in the prophylaxis or treatment of HIV infection in humans. Amongthe compounds approved for use in treating HIV infection and AIDS arenucleoside RT inhibitors (NRTI) such as 3′-azido-3′-deoxythymidine(AZT), 2′,3′-dideoxyinosine (ddl), 2′,3′-dideoxycytidine (ddC), d4T,3TC, abacavir, emtricitabine, and tenofovir disoproxil fumarate, as wellas non-nucleoside RT inhibitors (nNRTI) such as nevirapine, delavirdine,and efavirenz.

While each of the foregoing drugs is effective in treating HIV infectionand AIDS, there remains a need to develop additional HIV antiviral drugsincluding additional RT inhibitors. A particular problem is thedevelopment of mutant HIV strains that are resistant to the knowninhibitors. The use of anti-retrovirals to treat AIDS often leads toviruses that are less sensitive to the inhibitors. This resistance istypically the result of mutations that occur in the reversetranscriptase segment of the pol gene. The continued use of antiviralcompounds to prevent HIV infection will inevitably result in theemergence of new resistant strains of HIV. Accordingly, there is acontinuing need for new RT inhibitors that are effective against mutantHIV strains.

SUMMARY OF THE INVENTION

The present invention is directed to 4′-substituted nucleosidederivatives and their use in the inhibition of HIV reversetranscriptase, the prophylaxis of infection by HIV, the treatment ofinfection by HIV, and the prophylaxis, treatment, and delay in the onsetor progression of AIDS and/or ARC.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to compounds having structural FormulaI:

-   or a pharmaceutically acceptable salt thereof, wherein:-   R is

-   X is O, S, CH₂ or CF₂;-   Y is —C≡C—R⁸ or —C≡N;-   R¹ is —H, —C(O)R⁶, —C(O)OR⁶, —C(O)N(R⁶)₂,

-   or a pro-drug modification of the mono-, di- or triphosphate;-   R² is —H, —C(O)R^(6a), —C(O)OR^(6a) or —C(O)N(R^(6a))₂;-   R³ is —H, —F, or —OH;-   R⁴ is —H, —C₁-C₆ alkyl, —C₂-C₆ alkenyl, —C₂-C₆ alkynyl, —C₁-C₆    haloalkyl, —C₃-C₇ cycloalkyl, 5- or 6-membered monocyclic    heteroaryl, a 9- or 10-membered bicyclic heteroaryl, halo, —CN,    —NO₂, —N(R^(X))₂, —NH(C₁-C₆ alkylene)-(5- or 6-membered monocyclic    heteroaryl), —NH(C₁-C₆ alkylene)-(9- or 10-membered bicyclic    heteroaryl), aryl, —NHC(O)OR^(6b), —N(C(O)OR^(6b))₂,    —NHC(O)N(R^(6b))₂, or —NHC(O)R^(6b), wherein each of said —C₁-C₆    alkyl group, said —C₂-C₆ alkenyl group or said —C₂-C₆ alkynyl group    can be optionally substituted with halo;-   R⁵ is —H, —C₁-C₆ alkyl, —C₂-C₆ alkenyl, —C₂-C₆ alkynyl, —C₁-C₆    haloalkyl, —C₃-C₇ cycloalkyl, 5- or 6-membered monocyclic    heteroaryl, a 9- or 10-membered bicyclic heteroaryl, halo, —OR^(X),    —CN, —NO₂, —N(R^(X))₂, —NH(C₁-C₆ alkylene)-(5- or 6-membered    monocyclic heteroaryl), —NH(C₁-C₆ alkylene)-(9- or 10-membered    bicyclic heteroaryl), aryl, —NHC(O)OR^(6b), —N(C(O)OR^(6b))₂,    —NHC(O)N(R^(6b))₂, or —NHC(O)R^(6b), wherein each of said —C₁-C₆    alkyl group, said —C₂-C₆ alkenyl group or said —C₂-C₆ alkynyl group    can be optionally substituted with halo;-   R⁶, R^(6a) and R^(6b) are each independently selected at each    occurrence from —H, —C₁-C₆ alkyl, —C₁-C₆ haloalkyl, —(C₁-C₃    alkylene)_(m)-(C₃-C₇ cycloalkyl), —(C₁-C₃ alkylene)_(m)-(aryl),    —(C₁-C₃ alkylene)_(m)-(4 to 7-membered heterocycloalkyl), —(C₁-C₃    alkylene)_(m)-(5- or 6-membered monocyclic heteroaryl) or —(C₁-C₃    alkylene)_(m)-(9- or 10-membered bicyclic heteroaryl), wherein each    of said —C₁-C₆ alkyl, said C₃-C₇ cycloalkyl group, said aryl group,    said 4 to 7-membered heterocycloalkyl group, said -(5- or 6-membered    monocyclic heteroaryl group or said 9- or 10-membered bicyclic    heteroaryl group can be optionally substituted with R⁷;-   m is an integer selected from 0 (zero) or 1;-   R⁷ represents from one to five substituent groups, each    independently selected from —C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆    alkynyl, C₁-C₆ haloalkyl, aryl, or a 5-6-member heteroaryl;-   R⁸ is —H, —C₁-C₆ alkyl, —C₁-C₆ haloalkyl, —C₃-C₇ cycloalkyl, aryl,    5- or 6-membered monocyclic heteroaryl or 9- or 10-membered bicyclic    heteroaryl;-   R⁹ is —H, halo, —C₁-C₆ alkyl, —C₁-C₆ haloalkyl, —CN, —OR^(Y) or    —N(R^(Y))₂;-   R^(X) is independently selected at each occurrence from —H, —C₁-C₆    alkyl, —C₁-C₆ haloalkyl, aryl, or 5- or 6-membered monocyclic    heteroaryl;-   or when either or both of R⁴ or R⁵ is —N(R^(X))₂, each R^(X) may    optionally be joined together with the nitrogen to which they are    both attached to form a 5- or 6-membered monocyclic heteroaryl or 9-    or 10-membered bicyclic heteroaryl; and-   R^(Y) is —H, —C₁-C₆ alkyl or —C₁-C₆ haloalkyl;-   with the proviso that when X is O, Y is —C≡CH or —C≡N, R¹ is —H, R²    is —H, R⁴ is —NH₂, R⁵ is —H, —F, or —OH and R⁹ is —F, then R³ is not    —F.

In an embodiment of this invention referred to herein as Formula 1a arecompounds of Formula I, or a pharmaceutically acceptable salt thereof,wherein R is

and all other variables therein (R¹, R², X, Y, etc.) are as defined inFormula I.

In an embodiment of this invention are compounds of Formula I havingstructural Formula II or a pharmaceutically acceptable salt thereof:

wherein all variables therein (R¹, R², X, Y, etc.) are as defined inFormula I.

In another embodiment of this invention are compounds of Formula Ihaving structural Formula III or a pharmaceutically acceptable saltthereof:

wherein all variables therein (R¹, R², X, Y, etc.) are as defined inFormula I.

In another embodiment of this invention are compounds of Formula Ihaving structural Formula IV or a pharmaceutically acceptable saltthereof:

wherein all variables therein (R¹, R², X, Y, etc.) are as defined inFormula I.

In another embodiment of this invention are compounds of Formula Ihaving structural Formula V or a pharmaceutically acceptable saltthereof:

wherein all variables therein (R¹, R², X, Y, etc.) are as defined inFormula I.

In an embodiment of this invention referred to herein as Embodiment Aare compounds of Formula I, Ia, II, III, IV or V, or a pharmaceuticallyacceptable salt thereof, wherein:

-   X is O, S, CH₂ or CF₂;-   Y is —C≡C—R⁸ or —C≡N;-   R¹ is —H or

-   R² is —H;-   R³ is —H, —F, or —OH;-   R⁴ is —H, —C₁-C₆ alkyl, —C₂-C₆ alkenyl, —C₂-C₆ alkynyl, —C₁-C₆    haloalkyl, —C₃-C₇ cycloalkyl, 5- or 6-membered monocyclic    heteroaryl, a 9- or 10-membered bicyclic heteroaryl, halo, —CN,    —NO₂, —N(R^(X))₂, —NH(C₁-C₆ alkylene)-(5- or 6-membered monocyclic    heteroaryl), —NH(C₁-C₆ alkylene)-(9- or 10-membered bicyclic    heteroaryl), aryl, —NHC(O)OR^(6b), —N(C(O)OR^(6b))₂,    —NHC(O)N(R^(6b))₂, or —NHC(O)R^(6b), wherein each of said —C₁-C₆    alkyl group, said —C₂-C₆ alkenyl group or said —C₂-C₆ alkynyl group    can be optionally substituted with halo;-   R⁵ is —H, —C₁-C₆ alkyl, —C₂-C₆ alkenyl, —C₂-C₆ alkynyl, —C₁-C₆    haloalkyl, —C₃-C₇ cycloalkyl, a 5- or 6-membered monocyclic    heteroaryl, a 9- or 10-membered bicyclic heteroaryl, halo, —OR^(X),    —CN, —NO₂, —N(R^(X))₂, —NH(C₁-C₆ alkylene)-(5- or 6-membered    monocyclic heteroaryl), —NH(C₁-C₆ alkylene)-(9- or 10-membered    bicyclic heteroaryl) or aryl, wherein each of said —C₁-C₆ alkyl    group, said —C₂-C₆ alkenyl group or said —C₂-C₆ alkynyl group can be    optionally substituted with halo;-   R⁸ is —H, —C₁-C₆ alkyl, —C₁-C₆ haloalkyl, —C₃-C₇ cycloalkyl, aryl,    5- or 6-membered monocyclic heteroaryl or 9- or 10-membered bicyclic    heteroaryl;-   R⁹ is —H, halo, —C₁-C₆ alkyl, —C₁-C₆ haloalkyl, —CN, —OR^(Y), or    —N(R^(Y))₂;-   R^(X) is independently selected at each occurrence from —H, —C₁-C₆    alkyl, —C₁-C₆ haloalkyl, aryl, or 5- or 6-membered monocyclic    heteroaryl; or when either or both of R⁴ or R⁵ is —N(R^(X))₂, each    R^(X) may optionally be joined together with the nitrogen to which    they are both attached to form a 5- or 6-membered monocyclic    heteroaryl or 9- or 10-membered bicyclic heteroaryl; and-   R^(Y) is —H, —C₁-C₆ alkyl or —C₁-C₆ haloalkyl;-   and all other variables, e.g., R⁶, R^(6a), R^(6b), m, etc., are as    defined in Formula I.

In classes of Embodiment A are compounds of Formula I, Ia, II, III, IVor V, or a pharmaceutically acceptable salt thereof, wherein:

-   R¹ is-H;

-   or R¹ is

In an embodiment of this invention referred to herein as Embodiment Bare compounds of Formula I, Ia, II, III, IV or V, or a pharmaceuticallyacceptable salt thereof, wherein:

-   R¹ is —H, —C(O)R⁶, —C(O)OR⁶ or —C(O)N(R⁶)₂,

-   or a pro-drug modification of the mono-, di- or triphosphate;-   R² is —H, —C(O)R^(6a), —C(O)OR^(6a) or —C(O)N(R^(6a))₂; and-   R⁴ is —H, —C₁-C₆ alkyl, —C₂-C₆ alkenyl, —C₂-C₆ alkynyl, —C₁-C₆    haloalkyl, —C₃-C₇ cycloalkyl, 5- or 6-membered monocyclic    heteroaryl, a 9- or 10-membered bicyclic heteroaryl, halo, —CN,    —NO₂, —N(R^(X))₂, —NH(C₁-C₆ alkylene)-(5- or 6-membered monocyclic    heteroaryl), —NH(C₁-C₆ alkylene)-(9- or 10-membered bicyclic    heteroaryl), aryl, —NHC(O)OR^(6b), —N(C(O)OR^(6b))₂,    —NHC(O)N(R^(6b))₂, or —NHC(O)R^(6b), wherein each of said —C₁-C₆    alkyl group, said —C₂-C₆ alkenyl group or said —C₂-C₆ alkynyl group    can be optionally substituted with halo;-   R⁵ is —H, —C₁-C₆ alkyl, —C₂-C₆ alkenyl, —C₂-C₆ alkynyl, —C₁-C₆    haloalkyl, —C₃-C₇ cycloalkyl, 5- or 6-membered monocyclic    heteroaryl, a 9- or 10-membered bicyclic heteroaryl, halo, —OR^(X),    —CN, —NO₂, —N(R^(X))₂, —NH(C₁-C₆ alkylene)-(5- or 6-membered    monocyclic heteroaryl), —NH(C₁-C₆ alkylene)-(9- or 10-membered    bicyclic heteroaryl), aryl, —NHC(O)OR^(6b), —N(C(O)OR^(6b))₂,    —NHC(O)N(R^(6b))₂, or —NHC(O)R^(6b), wherein each of said —C₁-C₆    alkyl group, said —C₂-C₆ alkenyl group or said —C₂-C₆ alkynyl group    can be optionally substituted with halo;-   provided that one or more of R¹, R², R⁴ or R⁵ is selected as    follows:-   R¹ is —C(O)R⁶, —C(O)OR⁶, —C(O)N(R⁶)₂ or a pro-drug modification of    the mono-, di- or triphosphate; and/or-   R² is —C(O)R^(6a), —C(O)OR^(6a) or —C(O)N(R^(6a))₂; and/or-   R⁴ is —NHC(O)OR^(6b), —N(C(O)OR^(6b))₂, —NHC(O)N(R^(6b))₂, or    —NHC(O)R^(6b); and/or-   R⁵ is —NHC(O)OR^(6b), —N(C(O)OR^(6b))₂, —NHC(O)N(R^(6b))₂, or    —NHC(O)R^(6b);-   and all other variables, e.g., X, Y, R³, R⁶, R^(6a), R^(6b), m, R⁷,    R⁸, R⁹, R^(X), and R^(Y), are as defined in Formula I.

In another embodiment of this invention, referred to as Embodiment C,are compounds of Formula I, Ia, II, III, IV or V, or a pharmaceuticallyacceptable salt thereof, wherein:

X is O;

Y is —C≡CH or —C≡N;

R¹ is —H, —C(O)R⁶, —C(O)OR⁶, —C(O)N(R⁶)₂,

or a pro-drug modification of the mono-, di- or triphosphate;

R² is H, —C(O)R^(6a), —C(O)OR^(6a) or —C(O)N(R^(6a))₂, or particularlyit is —H;

R³ is —H, or —OH; or particularly R³ is —H;

R⁴ is —N(R^(X))₂, —NHC(O)OR^(6b) or —NHC(O)N(R^(6b))₂; or particularlyR⁴ is —N(R^(X))₂;

R⁵ is —H, halo, —C₁-C₆ alkyl, —OR^(X) or —N(R^(X))₂; and particularly R⁵is —H, —Cl, —F or —NH₂;

R⁶, R^(6a), and R^(6b) are each independently selected at eachoccurrence from —H, —C₁-C₆ alkyl, —C₁-C₆ haloalkyl, aryl (preferablyphenyl), or a 5- or 6-membered monocyclic heteroaryl, wherein R⁶,R^(6a), and R^(6b) are each optionally substituted with R⁷;

R⁷ is —C₁-C₆ alkyl, aryl (preferably phenyl) or 5-6 member monocyclicheteroaryl;

R⁸ is —H;

R⁹ is —H, halo, —C₁-C₃ alkyl, —C₁-C₃ haloalkyl, —CN, —OR^(Y), or—N(R^(Y))₂, and particularly it is —H, —F, —Cl, —I, —Br or —CH₃;

R^(X) is independently selected at each occurrence from —H, —C₁-C₆alkyl, —C₁-C₆ haloalkyl, aryl, or 5- or 6-membered monocyclicheteroaryl;

-   or when either or both of R⁴ or R⁵ is —N(R^(X))₂, each R^(X) may    optionally be joined together with the nitrogen to which they are    both attached to form a 5- or 6-membered monocyclic heteroaryl or 9-    or 10-membered bicyclic heteroaryl; and

R^(Y) is —H, —C₁-C₆ alkyl or —C₁-C₆ haloalkyl.

In another embodiment of this invention, referred to as Embodiment D,are compounds of Formula I, Ia, II, III, IV or V, or a pharmaceuticallyacceptable salt thereof, wherein:

-   -   X is O;    -   Y is —C≡CH or —C≡N;    -   R¹ is —H,

or a pro-drug modification of the mono-, di- or triphosphate;

R² is —H;

R³ is —H;

R⁴ is —NH₂;

R⁵ is —H, —Cl, —F or —NH₂;

R⁸ is —H; and

R⁹ is —H, —F, —Cl, —I, —Br, or —CH₃.

In another embodiment of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment A or B, or a pharmaceutically acceptablesalt thereof wherein X is O.

In another embodiment of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment A or B, or a pharmaceutically acceptablesalt thereof wherein Y is —C≡C—R⁸. In another embodiment are compoundsof Formula I, Ia, II, III, IV or V, or Embodiment A, B, C or D, or apharmaceutically acceptable salt thereof wherein Y is —C≡CH.

In another embodiment of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment A, B, C or D, or a pharmaceuticallyacceptable salt thereof, wherein Y is —C≡N.

In other embodiments of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment B or C, or a pharmaceutically acceptablesalt thereof, wherein: R¹ is —H, —C(O)R⁶, —C(O)OR⁶, —C(O)N(R⁶)₂, or apro-drug modification of

In other embodiments of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment A, B, C or D, or a pharmaceuticallyacceptable salt thereof, wherein

-   (a) R¹ is —H; or-   (b) R¹ is

or

-   (c) R¹ is

In other embodiments of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment B, C or D, or a pharmaceuticallyacceptable salt thereof, wherein:

-   (a) R¹ is

or a pro-drug modification of the mono-, di- or triphosphate;

-   or (b) R¹ is

or a pro-drug modification of the mono-, di- or triphosphate;

-   or (c) R¹ is

or a pro-drug modification of the triphosphate;

-   or (d) R¹ is a pro-drug modification of

In another embodiment of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment B or C, or a pharmaceutically acceptablesalt thereof, wherein R¹ is —H, —C(O)R⁶, —C(O)OR⁶, or —C(O)N(R⁶)₂, or apro-drug modification of the mono-, di- or triphosphate. In a classthereof, R¹ is —C(O)R⁶, —C(O)OR⁶, or —C(O)N(R⁶)₂ or a pro-drugmodification of the mono-, di- or triphosphate.

In other embodiments of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment B or C, or a pharmaceutically acceptablesalt thereof, wherein:

-   R² is —H, —C(O)R^(6a), —C(O)OR^(6a) or —C(O)N(R^(6a))₂;-   or R² is —C(O)R^(6a), —C(O)OR^(6a) or —C(O)N(R^(6a))₂;-   or R² is —H.

In another embodiment of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment A, B or C, or a pharmaceuticallyacceptable salt thereof, wherein R³ is —H or —OH. In a furtherembodiment are compounds of Formula I, Ia, II, III, IV or V, orEmbodiment A, B or C, or a pharmaceutically acceptable salt thereof,wherein R³ is —H.

In another embodiment of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment A or B, or a pharmaceutically acceptablesalt thereof, wherein R⁴ is —N(R^(X))₂, —NHC(O)OR^(6b),—N(C(O)OR^(6b))₂, —NHC(O)N(R^(6b))₂, or —NHC(O)R^(6b); and particularlyR⁴ is —N(R^(X))₂. More particularly R⁴ is —NH₂.

In other embodiments of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment B, or a pharmaceutically acceptable saltthereof, wherein:

-   R⁵ is —H, halo, —C₁-C₆ alkyl, —OR^(X), —N(R^(X))₂, —NHC(O)OR^(6b),    —N(C(O)OR^(6b))₂, —NHC(O)N(R^(6b))₂, or —NHC(O)R^(6b);-   or R⁵ is —NHC(O)OR^(6b), —N(C(O)OR^(6b))₂, —NHC(O)N(R^(6b))₂, or    —NHC(O)R^(6b);-   or R⁵ is —H, halo (preferably —F or —Cl), —C₁-C₆ alkyl, —OR^(X) or    —N(R^(X))₂;-   or R⁵ is —H, —Cl, —F or —NH₂.

In other embodiments of this invention are compounds of Embodiment A orB, or a pharmaceutically acceptable salt thereof, wherein:

-   R⁵ is —H, halo (preferably —F or —Cl), —C₁-C₆ alkyl, —OR^(X) or    —N(R^(X))₂;-   or R⁵ is —H, —Cl, —F or —NH₂.

In another embodiment of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment B, or a pharmaceutically acceptable saltthereof, wherein R⁶, R^(6a) and R^(6b) are each independently selectedat each occurrence from —H, —C₁-C₆ alkyl, —C₁-C₆ haloalkyl, aryl(preferably phenyl), or a 5- or 6-membered monocyclic heteroaryl. Inanother embodiment of this invention are compounds of Embodiment A, or apharmaceutically acceptable salt thereof, wherein R^(6b) is selected ateach occurrence from —H, —C₁-C₆ alkyl, —C₁-C₆ haloalkyl, aryl(preferably phenyl), or a 5- or 6-membered monocyclic heteroaryl.

In another embodiment of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment A or B, or a pharmaceutically acceptablesalt thereof, wherein R⁷ is —C₁-C₆ alkyl, aryl (preferably phenyl) or5-6 member monocyclic heteroaryl.

In another embodiment of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment A or B, or a pharmaceutically acceptablesalt thereof, wherein R⁸ is-H.

In another embodiment of this invention are compounds of Formula I, Ia,II, III, IV or V, or Embodiment A or B, or a pharmaceutically acceptablesalt thereof, wherein R⁹ is —H, halo, —C₁-C₃ alkyl, —C₁-C₃ haloalkyl,—CN, —OR^(Y), or —N(R^(Y))₂; and particularly it is —H, —F, —Cl, —I, —Bror —CH₃.

All structural Formulas, embodiments and classes thereof describedherein include the pharmaceutically acceptable salts of the compoundsdefined therein. Reference to the compounds of Formula I hereinencompasses the compounds of each of Formulas I, Ia, II III, IV or V,and all embodiments and classes thereof. Reference to the compounds ofthis invention as those of a specific formula or embodiment, e.g.,Formula I, Ia, II III, IV or V, or embodiments thereof, or any othergeneric structural formula or specific compound described or claimedherein, is intended to encompass the specific compound or compoundsfalling within the scope of the Formula or embodiment, including saltsthereof, particularly pharmaceutically acceptable salts, solvates(including hydrates) of such compounds and solvated salt forms thereof,where such forms are possible, unless specified otherwise.

The present invention includes each of the Examples described herein,and pharmaceutically acceptable salts thereof. The invention alsoencompasses pharmaceutical compositions comprising an effective amountof a compound of the invention or a pharmaceutically acceptable saltthereof, and a pharmaceutically acceptable carrier.

As used herein, the term “alkyl” refers to a monovalent straight orbranched chain, saturated aliphatic hydrocarbon radical having a numberof carbon atoms in the specified range. Thus, for example, “C₁₋₆ alkyl”(or “C₁-C₆ alkyl”) refers to any of the hexyl alkyl and pentyl alkylisomers as well as n-, iso-, sec- and t-butyl, n- and iso-propyl, ethyland methyl. As another example, “C₁₋₄ alkyl” refers to n-, iso-, sec-and t-butyl, n- and iso-propyl, ethyl and methyl.

The term “alkenyl” refers to a monovalent straight or branched chainaliphatic hydrocarbon radical containing one carbon-carbon double bondand having a number of carbon atoms in the specified range. Thus, forexample, “C₂₋₆ alkenyl” (or “C₂-C₆ alkenyl”) refers to all of thehexenyl and pentenyl isomers as well as 1-butenyl, 2-butenyl, 3-butenyl,isobutenyl, 1-propenyl, 2-propenyl, and ethenyl (or vinyl).

The term “alkynyl” refers to a monovalent straight or branched chainaliphatic hydrocarbon radical containing one carbon-carbon triple bondand having a number of carbon atoms in the specified range. Thus, forexample, “C₂₋₆ alkynyl” (or “C₂-C₆ alkynyl”) refers to all of thehexynyl and pentynyl isomers as well as 1-butynyl, 2-butynyl, 3-butynyl,1-propynyl, 2-propynyl, and ethynyl.

The term “alkylene” refers to any divalent linear or branched chainaliphatic hydrocarbon radical having a number of carbon atoms in thespecified range. Thus, for example, “—C₁₋₆ alkylene-” refers to any ofthe C₁ to C₆ linear or branched alkylenes, and “—C₁₋₃ alkylene-” refersto any of the C₁ to C₃ linear or branched alkylenes. A particular classof alkylenes includes —(CH₂)₁₋₃—, —(CH₂)₂₋₃, —(CH₂)₁₋₂—, and —CH₂—,—CH(CH₃)—, and —C(CH₃)₂—.

The term “cycloalkyl” refers to any monocyclic ring of an alkane havinga number of carbon atoms in the specified range. Thus, for example,“C₃₋₇ cycloalkyl” (or “C₃-C₇ cycloalkyl”) refers to cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl. A particular classof interest for compounds of Formula I and embodiments thereof is C₃₋₆cycloalkyl.

The term “halogen” (or “halo”) refers to fluorine, chlorine, bromine andiodine (alternatively referred to as fluoro, chloro, bromo, and iodo). Aparticular class of interest for compounds of Formula I and embodimentsthereof is each of fluoro of chloro.

The term “haloalkyl” refers to an alkyl group as defined above in whichone or more of the hydrogen atoms have been replaced with halo (i.e.,—F, —Cl, —Br and/or —I). Thus, for example, “C₁₋₆ haloalkyl” (or “C₁-C₆haloalkyl”) refers to a C₁ to C₆ linear or branched alkyl group asdefined above with one or more halo substituents. The term “fluoroalkyl”has an analogous meaning except that the halogen substituents arerestricted to fluoro. Suitable fluoroalkyls include the series(CH₂)₀₋₄CF₃ (i.e., trifluoromethyl, 2,2,2-trifluoroethyl,3,3,3-trifluoro-n-propyl, etc.). A fluoroalkyl of particular interest isCF₃.

The term “C(O)” refers to carbonyl. The terms “S(O)₂” and “SO₂” eachrefer to sulfonyl. The term “S(O)” refers to sulfinyl.

The term “aryl” (or “C₆-C₁₀ aryl”) refers to (i) phenyl, or (ii) 9- or10-membered bicyclic, fused carbocylic ring systems in which at leastone ring is aromatic. Suitable aryls include, for example, phenyl,naphthyl, tetrahydronaphthyl (tetralinyl), or indenyl. In a particularclass of compounds of Formula I and embodiments thereof, aryl is phenylor naphthyl, and more particularly aryl is phenyl.

The term “heteroaryl” refers to (i) a 5- or 6-membered heteroaromaticring containing from 1 to 4 heteroatoms independently selected from N, Oand S, wherein each N is optionally in the form of an oxide to theextent chemically possible, (ii) a 9- or 10-membered bicyclic fused ringsystem, wherein the fused ring system contains from 1 to 6 heteroatomsindependently selected from N, O and S, wherein each ring in the fusedring system contains zero, one, or more than one heteroatom, and atleast one ring is aromatic, and each N is optionally in the form of anoxide to the extent chemically possible, and each S in a ring which isnot aromatic is optionally S(O) or S(O)2. Suitable 5- and 6-memberedheteroaromatic rings include, for example, pyridyl, pyrrolyl, pyrazinyl,pyrimidinyl, pyridazinyl, triazinyl, thienyl, furanyl, imidazolyl,pyrazolyl, triazolyl triazolyl (i.e., 1,2,3-triazolyl or1,2,4-triazolyl), tetrazolyl, oxazolyl, isooxazolyl, oxadiazolyl (i.e.,the 1,2,3-, 1,2,4-, 1,2,5-(furazanyl), or 1,3,4-isomer), oxatriazolyl,thiazolyl, isothiazolyl, and thiadiazolyl. Suitable 9- and 10-memberedheterobicyclic, fused ring systems include, for example, benzofuranyl,indolyl, indazolyl, naphthyridinyl, isobenzofuranyl, benzopiperidinyl,benzisoxazolyl, benzoxazolyl, chromenyl, quinolinyl, isoquinolinyl,cinnolinyl, quinazolinyl, tetrahydro uinolinyl, tetrahydroisoquinolinyl,isoindolyl, benzodioxolyl (e.g., benzo-1,3-dioxolyl:

benzopiperidinyl, benzisoxazolyl, benzoxazolyl, chromanyl, isochromanyl,benzothienyl, benzofuranyl, imidazo[1,2-a]pyridinyl, benzotriazolyl,dihydroindolyl, dihydroisoindolyl, indazolyl, indolinyl, isoindolinyl,quinoxalinyl, quinazolinyl, 2,3-dihydrobenzofuranyl, and2,3-dihydrobenzo-1,4-dioxinyl (i.e.,

It is understood that the specific rings and ring systems suitable foruse in the present invention are not limited to those listed in thepreceding paragraphs. These rings and ring systems are merelyrepresentative. Unless expressly stated to the contrary in a particularcontext, any of the various cyclic rings and ring systems describedherein may be attached to the rest of the compound at any ring atom(i.e., any carbon atom or any heteroatom) provided that the attachmentis chemically allowed and a stable compound results.

Unless expressly depicted or described otherwise, a variable depicted ina structural formula with a “floating” bond attached to a ring, such asR⁹ in Formula I, is permitted to be a substituent (alternatively, R⁹ maybe —H) on any available carbon or nitrogen atom in the ring to which thevariable is attached.

When a moiety is noted as being “optionally substituted” in Formula I orany embodiment thereof, it means that Formula I or the embodimentthereof encompasses both compounds that are substituted with the notedsubstituent (or substituents) on the moiety and compounds that do notcontain the noted substituent (or substituents) on the moiety (i.e.,wherein the moiety is unsubstituted). As one example, when R⁴ is a—C₁-C₆ alkyl group that can be optionally substituted with halo, then R⁴can be —C₁-C₆ alkyl or —C₁-C₆ haloalkyl.

When any variable (e.g., R⁷, R^(X), R^(Y)) occurs more than one time inany constituent or in Formula I or in any other formula depicting anddescribing compounds of the present invention, its definition on eachoccurrence is independent of its definition at every other occurrence.Also, combinations of substituents and/or variables are permissible onlyif such combinations result in stable compounds.

Unless expressly stated to the contrary, substitution by a namedsubstituent is permitted on any atom in a ring (e.g., cycloalkyl, aryl,or heteroaryl) provided such ring substitution is chemically allowed andresults in a stable compound.

Unless expressly stated to the contrary, all ranges cited herein areinclusive. For example, a heteroaromatic ring described as containingfrom “1 to 4 heteroatoms” means the ring can contain 1, 2, 3 or 4heteroatoms. It is also to be understood that any range cited hereinincludes within its scope all of the sub-ranges within that range. Thus,for example, a heterocyclic ring described as containing from “1 to 4heteroatoms” is intended to include as aspects thereof, heterocyclicrings containing 2 to 4 heteroatoms, 3 or 4 heteroatoms, 1 to 3heteroatoms, 2 or 3 heteroatoms, 1 or 2 heteroatoms, 1 heteroatom, 2heteroatoms, 3 heteroatoms, or 4 heteroatoms. As another example, anaryl or heteroaryl described as optionally substituted with R⁷, whereinR⁷ is “from 1 to 5 substituent groups” is intended to include as aspectsthereof, the aryl or heteroaryl substituted with 1 to 5 substituents, 2to 5 substituents, 3 to 5 substituents, 4 to 5 substituents, 5substituents, 1 to 4 substituents, 2 to 4 substituents, 3 to 4substituents, 4 substituents, 1 to 3 substituents, 2 to 3 substituents,3 substituents, 1 to 2 substituents, 2 substituents, and 1 substituent.

In Embodiment B, “one or more of R¹, R², R⁴ or R⁵ is selected asfollows” includes only one of R¹, R², R⁴ or R⁵ as being defined as inthe proviso, or any combination of more than one of R¹, R², R⁴ and/or R⁵each being defined as in the proviso. For example, the followingcombinations of variables may be defined as in the proviso of EmbodimentB: R¹ and R²; R¹ and R⁴; R¹ and R⁵; R² and R⁴; R² and R⁵; R⁴ and R⁵; R¹,R² and R⁴; R¹, R² and R⁵; R¹, R⁴ and R⁵; R², R⁴ and R⁵; or R¹, R², R⁴and R⁵.

As would be recognized by one of ordinary skill in the art, certain ofthe compounds of the present invention can exist as tautomers. Alltautomeric forms of these compounds, whether isolated individually or inmixtures, are within the scope of the present invention. For example, ininstances where an —OH substituent is permitted on a heteroaromatic ringand keto-enol tautomerism is possible, it is understood that thesubstituent might in fact be present, in whole or in part, in the oxo(═O) form.

A “stable” compound is a compound which can be prepared and isolated andwhose structure and properties remain or can be caused to remainessentially unchanged for a period of time sufficient to allow use ofthe compound for the purposes described herein (e.g., therapeutic orprophylactic administration to a subject). The compounds of the presentinvention are limited to stable compounds embraced by Formula I and itsembodiments.

The compounds of Formula I may have one or more chiral (asymmetric)centers. The present invention encompasses all stereoisomeric forms ofthe compounds of Formula I. Centers of asymmetry that are present in thecompounds of Formula I can all independently of one another have (R) or(S) configuration. When bonds to a chiral carbon are depicted asstraight lines in the structural Formulas of the invention, or when acompound name is recited without an (R) or (S) chiral designation for achiral carbon, it is understood that both the (R) and (S) configurationsof each such chiral carbon, and hence each enantiomer or diastereomerand mixtures thereof, are embraced within the Formula or by the name.The production of specific stereoisomers or mixtures thereof may beidentified in the Examples where such stereoisomers or mixtures wereobtained, but this in no way limits the inclusion of all stereoisomersand mixtures thereof from being within the scope of this invention.

The invention includes all possible enantiomers and diastereomers andmixtures of two or more stereoisomers, for example mixtures ofenantiomers and/or diastereomers, in all ratios. Thus, enantiomers are asubject of the invention in enantiomerically pure form, both aslevorotatory and as dextrorotatory antipodes, in the form of racematesand in the form of mixtures of the two enantiomers in all ratios. In thecase of a cis/trans isomerism the invention includes both the cis formand the trans form as well as mixtures of these forms in all ratios. Thepreparation of individual stereoisomers can be carried out, if desired,by separation of a mixture by customary methods, for example bychromatography or crystallization, by the use of stereochemicallyuniform starting materials for the synthesis or by stereoselectivesynthesis. Optionally a derivatization can be carried out before aseparation of stereoisomers. The separation of a mixture ofstereoisomers can be carried out at an intermediate step during thesynthesis of a compound of Formula I or it can be done on a finalracemic product. Absolute stereochemistry may be determined by X-raycrystallography of crystalline products or crystalline intermediateswhich are derivatized, if necessary, with a reagent containing astereogenic center of known configuration. Alternatively, absolutestereochemistry may be determined by Vibrational Circular Dichroism(VCD) spectroscopy analysis. The present invention includes all suchisomers, as well as salts, solvates (which includes hydrates) andsolvated salts of such racemates, enantiomers, diastereomers andtautomers and mixtures thereof.

The atoms in a compound of Formula I may exhibit their natural isotopicabundances, or one or more of the atoms may be artificially enriched ina particular isotope having the same atomic number, but an atomic massor mass number different from the atomic mass or mass numberpredominantly found in nature. The present invention is meant to includeall suitable isotopic variations of the compounds of generic Formula I.For example, different isotopic forms of hydrogen (H) include protium(¹H) and deuterium (²H). Protium is the predominant hydrogen isotopefound in nature. Enriching for deuterium may afford certain therapeuticadvantages, such as increasing in vivo half-life or reducing dosagerequirements, or may provide a compound useful as a standard forcharacterization of biological samples. Isotopically-enriched compoundswithin generic Formula I can be prepared without undue experimentationby conventional techniques well known to those skilled in the art or byprocesses analogous to those described in the Schemes and Examplesherein using appropriate isotopically-enriched reagents and/orintermediates.

The compounds can be administered in the form of pharmaceuticallyacceptable salts. The term “pharmaceutically acceptable salt” refers toa salt which is not biologically or otherwise undesirable (e.g., isneither toxic nor otherwise deleterious to the recipient thereof).

When the compounds of Formula I contain one or more acidic or basicgroups the invention also includes the corresponding pharmaceuticallyacceptable salts. Thus, the compounds of Formula I which contain acidicgroups (e.g., —COOH or a phenolic group) can be used according to theinvention as, for example but not limited to, alkali metal salts,alkaline earth metal salts or as ammonium salts. Examples of such saltsinclude but are not limited to sodium salts, potassium salts, calciumsalts, magnesium salts or salts with ammonia or organic amines such as,for example, ethylamine, ethanolamine, triethanolamine or amino acids.Compounds of Formula I which contain one or more basic groups, i.e.groups which can be protonated, can be used according to the inventionin the form of their acid addition salts with inorganic or organic acidsas, for example but not limited to, salts with hydrogen chloride,hydrogen bromide, phosphoric acid, sulfuric acid, nitric acid,benzenesulfonic acid, methanesulfonic acid, p-toluenesulfonic acid,naphthalenedisulfonic acids, oxalic acid, acetic acid, trifluoroaceticacid, tartaric acid, lactic acid, salicylic acid, benzoic acid, formicacid, propionic acid, pivalic acid, diethylacetic acid, malonic acid,succinic acid, pimelic acid, fumaric acid, maleic acid, malic acid,sulfaminic acid, phenylpropionic acid, gluconic acid, ascorbic acid,isonicotinic acid, citric acid, adipic acid, etc. If the compounds ofFormula I simultaneously contain acidic and basic groups in the moleculethe invention also includes, in addition to the salt forms mentioned,inner salts or betaines (zwitterions). Salts can be obtained from thecompounds of Formula I by customary methods which are known to theperson skilled in the art, for example by combination with an organic orinorganic acid or base in a solvent or dispersant, or by anion exchangeor cation exchange from other salts. The present invention also includesall salts of the compounds of Formula I which, owing to lowphysiological compatibility, are not directly suitable for use inpharmaceuticals but which can be used, for example, as intermediates forchemical reactions or for the preparation of pharmaceutically acceptablesalts.

Another embodiment of the present invention is a compound of Formula Iwherein the compound or its salt is in a substantially pure form. Asused herein “substantially pure” means suitably at least about 60 wt. %,typically at least about 70 wt. %, preferably at least about 80 wt. %,more preferably at least about 90 wt. % (e.g., from about 90 wt. % toabout 99 wt. %), even more preferably at least about 95 wt. % (e.g.,from about 95 wt. % to about 99 wt. %, or from about 98 wt. % to 100 wt.%), and most preferably at least about 99 wt. % (e.g., 100 wt. %) of aproduct containing a compound of Formula I or its salt (e.g., theproduct isolated from a reaction mixture affording the compound or salt)consists of the compound or salt. The level of purity of the compoundsand salts can be determined using a standard method of analysis such asthin layer chromatography, gel electrophoresis, high performance liquidchromatography, and/or mass spectrometry. If more than one method ofanalysis is employed and the methods provide experimentally significantdifferences in the level of purity determined, then the method providingthe highest purity level governs. A compound or salt of 100% purity isone which is free of detectable impurities as determined by a standardmethod of analysis. With respect to a compound of the invention whichhas one or more asymmetric centers and can occur as mixtures ofstereoisomers, a substantially pure compound can be either asubstantially pure mixture of the stereoisomers or a substantially pureindividual diastereomer or enantiomer.

Furthermore, compounds of the present invention may exist in amorphousform and/or one or more crystalline forms, and as such all amorphous andcrystalline forms and mixtures thereof of the compounds of Formula I areintended to be included within the scope of the present invention. Inaddition, some of the compounds of the instant invention may formsolvates with water (i.e., a hydrate) or common organic solvents. Suchsolvates and hydrates, particularly the pharmaceutically acceptablesolvates and hydrates, of the instant compounds are likewise encompassedwithin the scope of this invention, along with un-solvated and anhydrousforms.

It is understood that a compound of Formula I (or any embodiment thereofand pharmaceutically acceptable salts thereof) wherein, for example, R¹is —H, —C(O)R⁶, —C(O)OR⁶, —C(O)N(R⁶)₂, or a pro-drug modification of themono-, di- or triphosphate, may be converted intracellularly/in vivo byone or more mechanisms (e.g., enzyme-catalyzed chemical reactions) tothe corresponding nucleoside 5′ triphosphate (i.e., wherein R¹ is—P(O)(OH)—O—P(O)(OH)—O—P(O)(OH)₂). While not wishing to be bound by anyparticular theory, the nucleoside 5′ triphosphate is generallyunderstood to be responsible for inhibiting the HIV RT enzyme and forthe resulting antiviral activity after administration of the compound ofFormula I to a subject.

Accordingly, prodrugs of the compounds of the invention are contemplatedherein. A discussion of prodrugs is provided in T. Higuchi and V.Stella, Pro-drugs as Novel Delivery Systems (1987) 14 of the A.C.S.Symposium Series, and in Bioreversible Carriers in Drug Design, (1987)Edward B. Roche, ed., American Pharmaceutical Association and PergamonPress. The term “prodrug” herein means a compound (e.g., a drugprecursor), which may be in the form of a pharmaceutically acceptablesalt, that is transformed intracellularly/in vivo to provide a4′-substituted Nucleoside Derivative which is an inhibitor of HIVreverse transcriptase. A nucleoside 5′ triphosphate is an example of a4′-substituted Nucleoside Derivative. The in vivo transformation mayoccur by various mechanisms, e.g., an enzyme-catalyzed chemicalreaction, a metabolic chemical reaction, and/or a spontaneous chemicalreaction (e.g., solvolysis), such as, for example, through hydrolysis inblood. This invention encompasses any prodrugs which convert, due tointracellular/in vivo conversion, to a 4′-substituted NucleosideDerivative of a compound of Formula I which is an inhibitor of HIVreverse transcriptase. For example, 4′-substituted NucleosideDerivatives of Formula I include, but are not limited to, compounds ofFormula I wherein:

a) R¹ is —P(O)(OH)—O—P(O)(OH)—O—P(O)(OH)₂;b). R¹ is —P(O)(OH)—O—P(O)(OH)—O—P(O)(OH)₂, and R² is —H; and/orc) R¹ is —P(O)(OH)—O—P(O)(OH)—O—P(O)(OH)₂, R² is —H, R⁴ is —NH₂ and R⁵is —H or —NH₂.

Prodrugs of compounds of Formula I can exhibit enhanced solubility,absorption, and/or lipophilicity compared to the compounds per se,thereby resulting in increased bioavailability and efficacy. When thecompound contains, for example, a hydroxy group, the prodrug can be aderivative of the hydroxy group such as an ester (—OC(O)R), a carbonateester (—OC(O)OR), a phosphate ester (—O—P(═O)(OH)₂), an ether (—OR), ora mono-phosphate prodrug such as a phosphoramidate (can be converted invivo to the corresponding nucleoside monophosphate).

For example, if a compound of Formula I contains an alcohol functionalgroup, a prodrug can be formed by the replacement of one or more of thehydrogen atoms of the alcohol groups with a group such as, for example,(C₁-C₆)alkanoyloxymethyl, 1-((C₁-C₆)alkanoyloxy)ethyl,1-methyl-1-((C₁-C₆)alkanoyloxy)ethyl, (C₁-C₆)alkoxycarbonyloxymethyl,N—(C₁-C₆)alkoxycarbonylaminomethyl, succinoyl, (C₁-C₆)alkanoyl,α-amino(C₁-C₄)alkyl, α-amino(C₁-C₄)alkylene-aryl, arylacyl andα-aminoacyl, or α-aminoacyl-α-aminoacyl, where each α-aminoacyl group isindependently selected from the naturally occurring L-amino acids, orglycosyl (the radical resulting from the removal of a hydroxyl group ofthe hemiacetal form of a carbohydrate).

The term “pro-drug modification of the mono-, di- or triphosphate” asused herein includes, but is not limited to, 5′-alcohol-derived prodrugssuch as —P(O)(—O—C₁-C₆alkyl)₂; —P(O)(—NH-(α-aminoacyl group))(—O-aryl),known as “McGuigan” type prodrugs; —P(O)(—O—(C₁-C₆alkylene)-S-acyl)(-NH-arylalkyl); S-acyl-2-thioethyl (SATE) prodrugs; acyclic phosphate ester that forms a bridge between two ribose hydroxylgroups, such as:

wherein the cyclic phosphate ester forms a bridge between the 3′-OHgroup and 5′-OH groups; and those described in U.S. Pat. No. 7,879,815;International Publication Nos. WO2005/003047, WO2008/082602,WO2010/0081628, WO2010/075517 and WO2010/075549; Mehellou, Chem. Med.Chem., 5:1841-1842 (2005); Bobeck et al., Antiviral Therapy 15:935-950(2010); Furman et al., Future Medicinal Chemistry, 1:1429-1452 (2009);and Erion, Microsomes and Drug Oxidations, Proceedings of theInternational Symposium, 17th, Saratoga Springs, N.Y., United States,Jul. 6-10, 2008, 7-12 (2008).

If a 4′-substituted derivative incorporates an amine functional group, aprodrug can be formed by the replacement of a hydrogen atom in the aminegroup with a group such as, for example, R-carbonyl-, RO-carbonyl-,NRR′-carbonyl- wherein R and R′ are each independently (C₁-C₁₀)alkyl,(C₃-C₇) cycloalkyl, benzyl, a natural α-aminoacyl, —C(OH)C(O)OY¹ whereinY¹ is H, (C₁-C₆)alkyl or benzyl, —C(OY²)Y³ wherein Y² is (C₁-C₄) alkyland Y³ is (C₁-C₆)alkyl; carboxy (C₁-C₆)alkyl; amino(C₁-C₄)alkyl ormono-N— or di-N,N—(C₁-C₆)alkylaminoalkyl; —C(Y⁴)Y⁵ wherein Y⁴ is H ormethyl and Y⁵ is mono-N— or di-N,N—(C₁-C₆)alkylamino morpholino;piperidin-1-yl or pyrrolidin-1-yl, and the like.

Pharmaceutically acceptable esters of the present compounds include thefollowing groups: (1) carboxylic acid esters obtained by esterificationof the hydroxy group of a hydroxyl compound, in which the non-carbonylmoiety of the carboxylic acid portion of the ester grouping is selectedfrom straight or branched chain alkyl (e.g., methyl, ethyl, n-propyl,isopropyl, t-butyl, sec-butyl or n-butyl), alkoxyalkyl (e.g.,methoxymethyl), aryl (e.g., benzyl), aryloxyalkyl (for example,phenoxymethyl), aryl (e.g., phenyl optionally substituted with, forexample, halogen, C₁₋₄alkyl, —O—(C₁₋₄alkyl) or amino); (2) sulfonateesters, such as alkyl- or aralkylsulfonyl (for example,methanesulfonyl); (3) amino acid esters (e.g., L-valyl or L-isoleucyl);(4) phosphonate esters and (5) mono-, di- or triphosphate esters. Thephosphate esters may be further esterified by, for example, a C₁₋₂₀alcohol or reactive derivative thereof, or by a 2,3-di (C₆₋₂₄)acylglycerol.

If a 4′-substituted deoxyribose derivative contains a carboxylic acidfunctional group, a prodrug can comprise an ester formed by thereplacement of the hydrogen atom of the acid group with a group such as,for example, (C₁-C₈)alkyl, (C₂-C₁₂)alkanoyloxymethyl,1-(alkanoyloxy)ethyl having from 4 to 9 carbon atoms,1-methyl-1-(alkanoyloxy)-ethyl having from 5 to 10 carbon atoms,alkoxycarbonyloxymethyl having from 3 to 6 carbon atoms,1-(alkoxycarbonyloxy)ethyl having from 4 to 7 carbon atoms,1-methyl-1-(alkoxycarbonyloxy)ethyl having from 5 to 8 carbon atoms,N-(alkoxycarbonyl)aminomethyl having from 3 to 9 carbon atoms,1-(N-(alkoxycarbonyl)amino)ethyl having from 4 to 10 carbon atoms,3-phthalidyl, 4-crotonolactonyl, gamma-butyrolacton-4-yl,di-N,N—(C₁-C₂)alkylamino(C₂-C₃)alkyl (such as β-dimethylaminoethyl),carbamoyl-(C₁-C₂)alkyl, N,N-di (C₁-C₂)alkylcarbamoyl-(C₁-C₂)alkyl andpiperidino-, pyrrolidino- or morpholino(C₂-C₃)alkyl, and the like.

Other examples include the following: when the compound of Formula I,contains a carboxylic acid group, the prodrug can be an ester or anamide, and when the compound of Formula I contains a primary amino groupor another suitable nitrogen that can be derivatized, the prodrug can bean amide, carbamate, urea, imine, or a Mannich base.

Conventional procedures for the selection and preparation of suitableprodrug derivatives are described, for example, in Design of Prodrugs,edited by H. Bundgaard, Elsevier, 1985; J. J. Hale et al., J. Med. Chem.2000, vol. 43, pp. 1234-1241; C. S. Larsen and J. Ostergaard, “Designand application of prodrugs” in: Textbook of Drug Design and Discovery,3rd edition, edited by C. S. Larsen, 2002, pp. 410-458; and Beaumont etal., Current Drug Metabolism 2003, vol. 4, pp. 461-458; the disclosuresof each of which are incorporated herein by reference in theirentireties.

Accordingly, the compounds within the generic structural formulas,embodiments and specific compounds described and claimed hereinencompass salts, all possible stereoisomers and tautomers, physicalforms (e.g., amorphous and crystalline forms), solvate and hydrate formsthereof and any combination of these forms, as well as the saltsthereof, pro-drug forms thereof which include any combination ofstereoisomer, tautomer, solvate, hydrate, salt and/or physical forms ofsaid pro-drugs, where such forms are possible unless specifiedotherwise.

The invention also encompasses methods for the treatment or prophylaxisof infection by HIV, for the inhibition of HIV reverse transcriptase,for the treatment, prophylaxis, or delay in the onset of AIDS in asubject in need thereof, which comprises administering to the subject aneffective amount of a compound of the invention or a pharmaceuticallyacceptable salt thereof.

The invention also encompasses a compound of the invention, or apharmaceutically acceptable salt thereof, for use in the preparation ofa medicament for the treatment or prophylaxis of infection by HIV, forthe inhibition of HIV reverse transcriptase, or for the treatment,prophylaxis, or delay in the onset of AIDS in a subject in need thereof.

The invention also encompasses a pharmaceutical composition comprisingan effective amount of a compound of the invention, or apharmaceutically acceptable salt thereof, and a pharmaceuticallyacceptable carrier and further comprising an effective amount of anadditional anti-HIV agent selected from the group consisting of HIVantiviral agents, immunomodulators, and anti-infective agents. Withinthis embodiment, the anti-HIV agent is an antiviral selected from thegroup consisting of HIV protease inhibitors, HIV reverse transcriptaseinhibitors, HIV integrase inhibitors, HIV fusion inhibitors, HIV entryinhibitors, and HIV maturation inhibitors.

Compounds of Formula Ia, II, III, IV or V, each form a subset of thecompounds included in Formula I. Any description above or which followsthat refers to a compound of Formula I also applies to a compound ofeach of Formula Ia, II, III, IV or V, and each embodiment thereof.

Other embodiments of the present invention include the following:

(a) A pharmaceutical composition comprising an effective amount of acompound of Formula I as defined above, or a prodrug or pharmaceuticallyacceptable salt thereof, and a pharmaceutically acceptable carrier.

(b) A pharmaceutical composition which comprises the product prepared bycombining (e.g., mixing) an effective amount of a compound of Formula Ias defined above, or a prodrug or pharmaceutically acceptable saltthereof, and a pharmaceutically acceptable carrier.

(c) The pharmaceutical composition of (a) or (b), further comprising aneffective amount of one or more an anti-HIV agents selected from thegroup consisting of HIV antiviral agents, immunomodulators, andanti-infective agents.

(d) The pharmaceutical composition of (c), wherein the anti-HIV agent isselected from one or more of an antiviral selected from the groupconsisting of HIV protease inhibitors, nucleoside HIV reversetranscriptase inhibitors, non-nucleoside HIV reverse transcriptaseinhibitors, HIV integrase inhibitors, HIV fusion inhibitors, HIV entryinhibitors and HIV maturation inhibitors.

(e) A combination which is (i) a compound of Formula I as defined above,or a prodrug or pharmaceutically acceptable salt thereof, and (ii) ananti-HIV agent selected from the group consisting of HIV antiviralagents, immunomodulators, and anti-infective agents; wherein thecompound and the anti-HIV agent are each employed in an amount thatrenders the combination effective for inhibition of HIV reversetranscriptase, for treatment or prophylaxis of infection by HIV, or fortreatment, prophylaxis of, or delay in the onset or progression of AIDS.

(f) The combination of (e), wherein the anti-HIV agent is an antiviralselected from the group consisting of HIV protease inhibitors,nucleoside HIV reverse transcriptase inhibitors, non-nucleoside HIVreverse transcriptase inhibitors, HIV integrase inhibitors, HIV fusioninhibitors, HIV entry inhibitors and HIV maturation inhibitors.

(g) A method for the inhibition of HIV reverse transcriptase in asubject in need thereof which comprises administering to the subject aneffective amount of a compound of Formula I or a prodrug orpharmaceutically acceptable salt thereof.

(h) A method for the prophylaxis or treatment of infection by HIV (e.g.,HIV-1) in a subject in need thereof which comprises administering to thesubject an effective amount of a compound of Formula I or a prodrug orpharmaceutically acceptable salt thereof.

(i) The method of (h), wherein the compound of Formula I is administeredin combination with an effective amount of at least one other HIVantiviral selected from the group consisting of HIV protease inhibitors,HIV integrase inhibitors, non-nucleoside HIV reverse transcriptaseinhibitors, nucleoside HIV reverse transcriptase inhibitors, HIV fusioninhibitors, HIV entry inhibitors and HIV maturation inhibitors.

(j) A method for the prophylaxis, treatment or delay in the onset orprogression of AIDS in a subject in need thereof which comprisesadministering to the subject an effective amount of a compound ofFormula I or a prodrug or pharmaceutically acceptable salt thereof.

(k) The method of (j), wherein the compound is administered incombination with an effective amount of at least one other HIV antiviralselected from the group consisting of HIV protease inhibitors, HIVintegrase inhibitors, non-nucleoside HIV reverse transcriptaseinhibitors, nucleoside HIV reverse transcriptase inhibitors, HIV fusioninhibitors, HIV entry inhibitors and HIV maturation inhibitors.

(l) A method for the inhibition of HIV reverse transcriptase in asubject in need thereof which comprises administering to the subject thepharmaceutical composition of (a), (b), (c) or (d) or the combination of(e) or (f).

(m) A method for the prophylaxis or treatment of infection by HIV (e.g.,HIV-1) in a subject in need thereof which comprises administering to thesubject the pharmaceutical composition of (a), (b), (c) or (d) or thecombination of (e) or (f).

(n) A method for the prophylaxis, treatment, or delay in the onset orprogression of AIDS in a subject in need thereof which comprisesadministering to the subject the pharmaceutical composition of (a), (b),(c) or (d) or the combination of (e) or (f).

The present invention also includes a compound of Formula I orpharmaceutically acceptable salt thereof, (i) for use in, (ii) for useas a medicament for, or (iii) for use in the preparation of a medicamentfor: (a) therapy (e.g., of the human body), (b) medicine, (c) inhibitionof HIV reverse transcriptase, (d) treatment or prophylaxis of infectionby HIV, or (e) treatment, prophylaxis of, or delay in the onset orprogression of AIDS. In these uses, the compounds of the presentinvention can optionally be employed in combination with one or moreanti-HIV agents selected from HIV antiviral agents, anti-infectiveagents, and immunomodulators.

Additional embodiments of the invention include the pharmaceuticalcompositions, combinations and methods set forth in (a)-(n) above andthe uses (i)(a)-(e) through (iii)(a)-(e) set forth in the precedingparagraph, wherein the compound of the present invention employedtherein is a compound of one of the embodiments, aspects, classes,sub-classes, or features described above. In all of these embodimentsetc., the compound may optionally be used in the form of a prodrug orpharmaceutically acceptable salt or pharmaceutically acceptable salt ofa prodrug.

Additional embodiments of the present invention include each of thepharmaceutical compositions, combinations, methods and uses set forth inthe preceding paragraphs, wherein the compound of the present inventionor its salt employed therein is substantially pure. With respect to apharmaceutical composition comprising a compound of Formula I or itsprodrug or salt and a pharmaceutically acceptable carrier and optionallyone or more excipients, it is understood that the term “substantiallypure” is in reference to a compound of Formula I or its prodrug and/orsalt per se.

Still additional embodiments of the present invention include thepharmaceutical compositions, combinations and methods set forth in(a)-(n) above and the uses (i)(a)-(e) through (iii)(a)-(e) set forthabove, wherein the HIV of interest is HIV-1. Thus, for example, in thepharmaceutical composition (d), the compound of Formula I is employed inan amount effective against HIV-1 and the anti-HIV agent is an HIV-1antiviral selected from the group consisting of HIV-1 proteaseinhibitors, HIV-1 reverse transcriptase inhibitors, HIV-1 integraseinhibitors, HIV-1 fusion inhibitors and HIV-1 entry inhibitors. Thecompounds of Formula I may also be useful agents against HIV-2.

The term “administration” and variants thereof (e.g., “administering” acompound) in reference to a compound of Formula I means providing thecompound to the individual in need of treatment or prophylaxis andincludes both self-administration and administration to the patient byanother person. When a compound or a prodrug thereof is provided incombination with one or more other active agents (e.g., antiviral agentsuseful for treating or prophylaxis of HIV infection or AIDS),“administration” and its variants are each understood to includeprovision of the compound or prodrug and other agents at the same timeor at different times. When the agents of a combination are administeredat the same time, they can be administered together in a singlecomposition or they can be administered separately.

As used herein, the term “composition” is intended to encompass aproduct comprising the specified ingredients, as well as any productwhich results from combining the specified ingredients. Ingredientssuitable for inclusion in a pharmaceutical composition arepharmaceutically acceptable ingredients, which means the ingredientsmust be compatible with each other and not deleterious to the recipientthereof. By “pharmaceutically acceptable” is meant that the ingredientsof the pharmaceutical composition must be compatible with each other andnot deleterious to the recipient thereof.

The term “subject” as used herein refers to an animal, preferably amammal, most preferably a human, who has been the object of treatment,observation or experiment.

The term “effective amount” as used herein means an amount sufficient toinhibit HIV reverse transcriptase, inhibit HIV replication, exert aprophylactic effect, and/or a exert a therapeutic effect afteradministration. One embodiment of “effective amount” is a“therapeutically effective amount” which is an amount of a compound thatis effective for inhibiting HIV reverse transcriptase, inhibiting HIVreplication (either of the foregoing which may also be referred toherein as an “inhibition effective amount”), treating HIV infection,treating AIDS, delaying the onset of AIDS, and/or slowing progression ofAIDS in a patient. Another embodiment of “effective amount” is a“prophylactically effective amount” which is an amount of the compoundthat is effective for prophylaxis of HIV infection or prophylaxis ofAIDS in a patient. It is understood that an effective amount cansimultaneously be both a therapeutically effective amount, e.g., fortreatment of HIV infection, and a prophylactically effective amount,e.g., for prevention or reduction of risk for developing AIDS. When thecompound of Formula I is administered as a salt, reference to an amountof the compound is to the free form (i.e., the non-salt form) of thecompound.

In the method of the present invention (i.e., inhibiting HIV reversetranscriptase, treating or prophylaxis of HIV infection, inhibiting HIVreplication, treating or prophylaxis of AIDS, delaying the onset ofAIDS, or delaying or slowing progression of AIDS), the compounds of thisinvention, optionally in the form of a salt, can be administered bymeans that produces contact of the active agent with the agent's site ofaction. They can be administered by conventional means available for usein conjunction with pharmaceuticals, either as individual therapeuticagents or in a combination of therapeutic agents. They can beadministered alone, but typically are administered with a pharmaceuticalcarrier selected on the basis of the chosen route of administration andstandard pharmaceutical practice. The compounds of the invention can,for example, be administered orally, parenterally (includingsubcutaneous injections, intravenous, intramuscular, intrasternalinjection or infusion techniques), by inhalation spray, or rectally, inthe form of a unit dosage of a pharmaceutical composition containing aneffective amount of the compound and conventional non-toxicpharmaceutically acceptable carriers, adjuvants and vehicles, any ofwhich administration methods can be provided as a single dose,once-daily, or less frequently such as once weekly or once monthly in,for example but not limited to, the dosage ranges and amounts describedbelow. Liquid preparations suitable for oral administration (e.g.,suspensions, syrups, elixirs and the like) can be prepared according totechniques known in the art and can employ any of the usual media suchas water, glycols, oils, alcohols and the like. Solid preparationssuitable for oral administration (e.g., powders, pills, capsules andtablets) can be prepared according to techniques known in the art andcan employ such solid excipients as starches, sugars, kaolin,lubricants, binders, disintegrating agents and the like. Parenteralcompositions can be prepared according to techniques known in the artand typically employ sterile water as a carrier and optionally otheringredients, such as a solubility aid. Injectable solutions can beprepared according to methods known in the art wherein the carriercomprises a saline solution, a glucose solution or a solution containinga mixture of saline and glucose. Further description of methods suitablefor use in preparing pharmaceutical compositions for use in the presentinvention and of ingredients suitable for use in said compositions isprovided in Remington's Pharmaceutical Sciences, 18th edition, edited byA. R. Gennaro, Mack Publishing Co., 1990 and in Remington—The Scienceand Practice of Pharmacy, 22nd Edition, published by PharmaceuticalPress and Philadelphia College of Pharmacy at University of theSciences, 2012, ISBN 978 0 85711-062-6 and prior editions.

Formulations of compounds described by Formula I that result in drugsupersaturation and/or rapid dissolution may be utilized to facilitateoral drug absorption. Formulation approaches to cause drugsupersaturation and/or rapid dissolution include, but are not limitedto, nanoparticulate systems, amorphous systems, solid solutions, soliddispersions, and lipid systems. Such formulation approaches andtechniques for preparing them are well known in the art. For example,solid dispersions can be prepared using excipients and processes asdescribed in reviews (e.g., A. T. M. Serajuddin, J Pharm Sci, 88:10, pp.1058-1066 (1999)). Nanoparticulate systems based on both attrition anddirect synthesis have also been described in reviews such as Wu et al(F. Kesisoglou, S. Panmai, Y. Wu, Advanced Drug Delivery Reviews, 59:7pp. 631-644 (2007)).

The compounds of Formula I, and pharmaceutically acceptable saltsthereof, are HIV reverse transcriptase inhibitors. The compounds areuseful for inhibiting HIV reverse transcriptase and for inhibiting HIVreplication in vitro and in vivo. More particularly, the compounds ofFormula I inhibit the polymerase function of HIV-1 reversetranscriptase. The testing of compounds of the Examples of the inventionin the assay set forth in the RT Polymerase Assay below, illustrates theability of compounds of the invention to inhibit the RNA-dependent DNApolymerase activity of HIV-1 reverse transcriptase. The compounds ofFormula I may also be useful agents against HIV-2.

The compounds of Formula I can be administered in a dosage range of0.001 to 1000 mg/kg of mammal (e.g., human) body weight per day, or atother time intervals as appropriate, in a single dose or in divideddoses. One example of a dosage range is 0.01 to 500 mg/kg body weightper day, or at other time intervals as appropriate, administered orallyor via other routes of administration in a single dose or in divideddoses. Another example of a dosage range is 0.1 to 100 mg/kg body weightper day, or at other time intervals as appropriate, administered orallyor via other routes of administration in single or divided doses. Fororal (e.g., tablets or capsules) or other routes of administration, thecompositions can be provided containing 1.0 to 500 milligrams of theactive ingredient, particularly 1, 5, 10, 15, 20, 25, 50, 75, 100, 150,200, 250, 300, 400, and 500 milligrams of the active ingredient for thesymptomatic adjustment of the dosage to the patient to be treated. Thespecific dose level and frequency of dosage for any particular patientmay be varied and will depend upon a variety of factors including theactivity of the specific compound employed, the metabolic stability andlength of action of that compound, the age, body weight, general health,sex, diet, mode and time of administration, rate of excretion, drugcombination, the severity of the particular condition, and the hostundergoing therapy. In some cases, depending on the potency of thecompound or the individual response, it may be necessary to deviateupwards or downwards from the given dose. Compounds of the invention canbe administered as a single dose, once-daily, or less frequently such asonce weekly or once monthly in, for example but not limited to, thedosage ranges and amounts noted above. Furthermore, the compound may beformulated for immediate or modified release such as extended orcontrolled release.

As noted above, the present invention is also directed to use of acompound of Formula I with one or more anti-HIV agents. An “anti-HIVagent” is any agent which is directly or indirectly effective in theinhibition of HIV, the treatment or prophylaxis of HIV infection, and/orthe treatment, prophylaxis or delay in the onset or progression of AIDS.It is understood that an anti-HIV agent is effective in treating,preventing, or delaying the onset or progression of HIV infection orAIDS and/or diseases or conditions arising therefrom or associatedtherewith. For example, the compounds of this invention may beeffectively administered, whether at periods of pre-exposure and/orpost-exposure, in combination with effective amounts of one or moreanti-HIV agents selected from HIV antiviral agents, imunomodulators,antiinfectives, or vaccines useful for treating HIV infection or AIDS.Suitable HIV antivirals for use in combination with the compounds of thepresent invention include, for example, those listed in Table 1 asfollows:

TABLE 1 Antiviral Agents for Treating HIV infection or AIDS Name Typeabacavir, ABC, Ziagen ® nRTI abacavir + lamivudine, Epzicom ® nRTIabacavir + lamivudine + zidovudine, Trizivir ® nRTI amprenavir,Agenerase ® PI atazanavir, Reyataz ® PI AZT, zidovudine, azidothymidine,Retrovir ® nRTI capravirine nnRTI darunavir, Prezista ® PI ddC,zalcitabine, dideoxycytidine, Hivid ® nRTI ddI, didanosine,dideoxyinosine, Videx ® nRTI ddI (enteric coated), Videx EC ® nRTIdelavirdine, DLV, Rescriptor ® nnRTI dolutegravir, Tivicay ® InIdoravirine, MK-1439 nnRTI efavirenz, EFV, Sustiva ®, Stocrin ® nnRTIefavirenz + emtricitabine + tenofovir DF, Atripla ® nnRTI + nRTI EFdA(4′-ethynyl-2-fluoro-2′-deoxyadenosine) nRTI Elvitegravir InIemtricitabine, FTC, Emtriva ® nRTI emtricitabine + tenofovir DF,Truvada ® nRTI emvirine, Coactinon ® nnRTI enfuvirtide, Fuzeon ® FIenteric coated didanosine, Videx EC ® nRTI etravirine, TMC-125 nnRTIfosamprenavir calcium, Lexiva ® PI indinavir, Crixivan ® PI lamivudine,3TC, Epivir ® nRTI lamivudine + zidovudine, Combivir ® nRTI lopinavir PIlopinavir + ritonavir, Kaletra ® PI maraviroc, Selzentry ® EInelfinavir, Viracept ® PI nevirapine, NVP, Viramune ® nnRTI PPL-100(also known as PL-462) (Ambrilia) PI raltegravir, MK-0518, Isentress ™InI Rilpivirine nnRTI ritonavir, Norvir ® PI saquinavir, Invirase ®,Fortovase ® PI stavudine, d4T,didehydrodeoxythymidine, Zerit ® nRTItenofovir DF (DF = disoproxil fumarate), TDF, Viread ® nRTI Tenofovir,hexadecyloxypropyl (CMX-157) nRTI Tenofovir alafenamide fumarate(GS-7340) nRTI tipranavir, Aptivus ® PI vicriviroc EI EI = entryinhibitor; FI = fusion inhibitor; InI = integrase inhibitor; PI =protease inhibitor; nRTI = nucleoside reverse transcriptase inhibitor;nnRTI = non-nucleoside reverse transcriptase inhibitor. Some of thedrugs listed in the table are used in a salt form; e.g., abacavirsulfate, delavirdine mesylate, indinavir sulfate, atazanavir sulfate,nelfinavir mesylate, saquinavir mesylate.

It is understood that the scope of combinations of the compounds of thisinvention with anti-HIV agents is not limited to the HIV antiviralslisted in Table A, but includes in principle any combination with anypharmaceutical composition useful for the treatment or prophylaxis ofAIDS. The HIV antiviral agents and other agents will typically beemployed in these combinations in their conventional dosage ranges andregimens as reported in the art, including, for example, the dosagesdescribed in the Physicians' Desk Reference, Thomson PDR, Thomson PDR,57th edition (2003), the 58th edition (2004), or the 59th edition (2005)and the current Physicians' Desk Reference (68th ed.). (2014), Montvale,N.J.: PDR Network. The dosage ranges for a compound of the invention inthese combinations can be the same as those set forth above.

The compounds of this invention are also useful in the preparation andexecution of screening assays for antiviral compounds. For example, thecompounds of this invention are useful for isolating enzyme mutants,which are excellent screening tools for more powerful antiviralcompounds. Furthermore, the compounds of this invention are useful inestablishing or determining the binding site of other antivirals to HIVreverse transcriptase, e.g., by competitive inhibition.

Abbreviations and acronyms employed herein include the following:

ACN = acetonitrile AcOH = acetic acid CHAPS = 3-((3-Cholamidopropyl)dimethylammonio)-1- Propanesulfonic CSH = Charge SurfaceHybrid DAST = (diethylamino)sulfur trifluoride DCE = 1,2-dichloroethaneDCM = dichloromethane DEAD = diethyl azodicarboxylate DIBAL-H =diisobutylaluminum hydride DIPEA = diisopropylethylamine DMF =N,N-dimethylformamide Dess-Martin periodinane = 1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxo1-3(1H)-one DMAP = 4-dimethylaminopyridineDMSO = dimethyl sulfoxide EDTA = ethylenediaminetetraacetic acid EtOAc =ethyl acetate EA = ethyl acetate EGTA = ethylene glycol tetraacetic acidEtOH = ethanol FBS = fetal bovine serum HIV = human immunodeficiencyvirus HPLC = high performance liquid chromatography hr = hour h = hourHz = hertz IBX = 2-iodoxybenzoic acid LCAP = liquid chromatography areapercent LCMS or LC-MS = liquid chromatography- mass spectroscopy L =liter LDA = lithium diisopropylamide LiHMDS = lithiumhexamethyldisilazide aq = aqueous AIBN = azobisisobutyronitrile m-CPBA =3-chloroperbenzoic acid Me = methyl MeOH = methanol Me-THF =2-methyltetrahydrofuran min = minute MHz = megahertz mL or ml =milliliter mol = moles mmol = millimoles NaH = sodium hydride NBS =N-bromosuccinimide NIS-N-iodosuccinimide NHS = normal human serum NMP =N-methyl-2-pyrrolidinone NMR = nuclear magnetic resonance NTP =nucleoside triphosphate dNTP = 2′-deoxy nucleoside triphosphate PBS =phosphate buffered saline PE, pet. ether = petroleum ether Ppm = partsper million PPTS = 4-toluenesulfonic acid r.t. = room temperature RT =reverse transcriptase TBAF = tetrabutylammonium fluoride t-BuOH =tert-butanol TEA = triethylamine THF = tetrahydrofuran TFA =trifluoroacetic acid TLC = thin layer chromatography TBS-Cl =t-butyldimethylsilyl chloride TBDMS-Cl = t-butyldimethylsilyl chlorideTMSCl = trimethylsilyl chloride

Compounds of the invention can be prepared by methods well known in theart of organic chemistry. See, for example, J. March, ‘Advanced OrganicChemistry’ 6th Edition, John Wiley and Sons. During synthetic sequencesit may be necessary and/or desirable to protect sensitive or reactivegroups on any of the molecules concerned. This is achieved by means ofconventional protecting groups, such as those described in T. W. Greeneand P. G. M. Wutts ‘Protective Groups in Organic Synthesis’ 4th Edition,John Wiley and Sons. The protective groups are optionally removed at aconvenient subsequent stage using methods well known in the art.

The compounds of the present invention can be readily prepared accordingto the following reaction schemes and examples, or modificationsthereof, using readily available starting materials, reagents andconventional synthesis procedures. In these reactions, it is alsopossible to make use of variants which are themselves known to those ofordinary skill in this art, but are not mentioned in greater detail.Furthermore, other methods for preparing compounds of the invention willbe readily apparent to the person of ordinary skill in the art in lightof the following reaction schemes and examples. Unless otherwiseindicated, all variables are as defined above.

Lactol 1-1 can be converted to 1-2 using methanolic HCl. The hydroxygroups of intermediate 1-2 can then be protected followed by theconversion of the 1′-OMe to 1′-Cl using HCl gas to provide 1-4.Intermediate 1-4 can be reacted with different substituted heterocycles(1-5) in the presence of a suitable base to provide intermediate 1-6.The 6-chloro of intermediate 1-6 can be converted to R⁴ using suitablechemistry followed by deprotection of the hydroxyl groups to provideintermediate 1-7. Intermediate 1-7 can be differentially protected toprovide 1-8. Oxidation of 1-8 provides aldehyde 1-9 which can thenundergo an aldol reaction with formaldehyde followed by reduction toprovide 1-10. Selective oxidation of the alpha face hydroxy groupfollowed by conversion of the aldehyde to the alkyne provides 1-11.Final deprotection of the 3′-alcohol provides targets 1-13.

Lactone 2-1 can be treated with the anion of different heterocycles toprovide intermediates of type 2-2. Intermediate 2-2 can be converted to2-3 by treatment with acid in the presence of silanes. Deprotection of2-3 followed by differential protection of the 3′ and 5′ hydroxylsprovides 2-5. Deoxygenation of 2-5 provides 2-6 which can then bedeprotected followed by differential protection to provide 2-8.Oxidation of the terminal alcohol to 2-9 followed by aldol reaction withformaldehyde and reduction provides the 2-10. Selective oxidation of thealpha face alcohol provides aldehyde 2-11 which can then be converted tothe acetylene 2-12. Global deprotection affords 2-13.

Intermediates of type 3-1 (synthesized using methods in scheme 1) areconverted to oximes of type 3-2. Dehydration of the oxime leads tocompounds 3-3 which can undergo final deprotection to provide targets3-4.

Intermediates of type 4-1 (synthesized using methods in scheme 2) areconverted to oximes of type 4-2. Dehydration of the oxime leads tocompounds 4-3 which can undergo final deprotection to provide targets4-4.

Intermediates of type 5-1 (Synthesized using methods from previousschemes) can be converted to the triphosphates 5-2 using literatureknown methods.

Intermediates of type 6-1 (Synthesized using methods from previousschemes) can be converted to the triphosphates 6-2 using literatureknown methods.

General Chemical Procedures:

All reagents were either purchased from common commercial sources orsynthesized according to literature procedures beginning from commercialreagents. Commercial reagents were used without further purification.Unless otherwise indicated, percent is percent by weight given thecomponent and the total weight of the composition, temperature is in °C. or is at ambient temperature and pressure is at or near atmospheric.1H NMR spectra were obtained on a Varian VNMR System 400 (400 MHz) andare reported as ppm downfield from Me₄Si with number of protons,multiplicities, and coupling constants in Hertz indicatedparenthetically. Where LC/MS data are presented, analyses was performedusing an Agilent 6110A MSD or an Applied Biosystems API-100 massspectrometer. The parent ion is given. Preparative HPLC was performed ona Waters preparative HPLC system fitted with a Waters Xselect.C18column, typically using gradient elution with water/acetonitrilecontaining 0.075% trifluoro acetic acid. Flash column chromatography wasperformed using pre-packed normal phase silica from Biotage, Inc. orbulk silica from Fisher Scientific. Unless otherwise indicated, columnchromatography was performed using a gradient elution of petroleumether/ethyl acetate, from petroleum ether 100% to 100% ethyl acetate.The term “room temperature” in the examples refers to the ambienttemperature which was typically in the range of about 20° C. to about26° C.

Intermediate A(2R,3S,5R)-5-chloro-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (Intermediate A)

Step 1: Synthesis of(2R,3S)-2-(hydroxymethyl)-5-methoxytetrahydrofuran-3-ol

To a stirred solution of(4S,5R)-5-(hydroxymethyl)tetrahydrofuran-2,4-diol (7.0 g, 52.2 mmol) inanhydrous methanol (105 mL) under argon atmosphere, was added acetylchloride (0.614 g, 7.83 mmol) dropwise with stirring at 0° C. over 5minutes and the resulting mixture was stirred at 0° C. for 3 hours. Thensolid sodium bicarbonate was added to neutralize the reaction mixture.The organic phase was collected by filtration and then concentratedunder reduced pressure to give a residue as syrup. The residue waspurified by silica gel (100-200 mesh) chromatography withdichloromethane/methanol (20/1) to give the title compound. ¹H-NMR: (300MHz, CDCl₃, ppm): δ 4.98-5.04 (m, 1H), 4.21-4.23 (m, 0.4H), 4.07-4.09(m, 0.6H), 3.83-3.89 (m, 1H), 3.50-3.66 (m, 2H), 3.27-3.32 (m, 3H),2.23-2.29 (m, 0.6H), 2.08-2.12 (m, 0.4H), 1.98-2.03 (m, 0.4H), 1.77-1.83(m, 0.6H).

Step 2: Synthesis of(2R,3S)-5-methoxy-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

To a stirred solution of(2R,3S)-2-(hydroxymethyl)-5-methoxytetrahydrofuran-3-ol (6.5 g, 43.9mmol) in dry pyridine (45 mL) under argon atmosphere, was added4-methylbenzoyl chloride (20.35 g, 132 mmol) dropwise at 0° C. overperiod of 15 minutes. The resulting mixture was gradually warmed to 30°C. and then stirred for 16 hours. The resulting solution wasconcentrated under reduced pressure. The resulting residue was dilutedwith ethyl acetate (400 mL), and then washed with aqueous hydrogenchloride (1 mol/L, 2×100 mL), saturated aqueous sodium bicarbonate(2×100 mL) and brine (100 mL) respectively. The organic phase wascollected, dried over anhydrous sodium sulfate, filtered andconcentrated under reduced pressure. The residue was purified by silicagel (100-200 mesh) chromatography with petroleum ether/ethyl acetate(20:1) to give the title compound. 1H-NMR: (300 MHz, CDCl₃, ppm): δ7.90-7.99 (m, 4H), 7.20-7.26 (m, 4H), 5.58-5.61 (m, 0.47H), 5.39-5.42(m, 0.55H), 5.18-5.24 (m, 1H), 4.46-4.65 (m, 3H), 3.43 (s, 1.61H), 3.36(s, 1.33H), 2.52-2.60 (m, 1H), 2.17-2.43 (m, 7H).

Step 3:(2R,3S,5R)-5-chloro-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (Intermediate A)

To a stirred solution of(2R,3S)-5-methoxy-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (4.0 g, 10.41 mmol) in anhydrous diethyl ether (20 mL)in a 100 mL three necked round-bottom flask, was introduced HCl (g). Theproduct was gradually precipitated out over period of 40 min at 0° C.The solid was filtered and washed with dry diethyl ether (3×20 mL),dried under high vacuum for 2 hours to give Intermediate A as a solid.1H-NMR: (300 MHz, CDCl₃, ppm): δ 7.96 (d, J=9.0 Hz, 2H), 7.90 (d, J=8.1Hz, 2H), 7.19-7.27 (m, 4H), 6.47 (d, J=5.1 Hz, 1H), 5.54-5.58 (m, 1H),4.85 (dd, J=3.3 Hz, J=7.2 Hz, 1H), 4.68 (dd, J=3.3 Hz, J=12.0 Hz, 1H),4.59 (dd, J=4.2 Hz, J=12.0 Hz, 1H), 2.83-2.92 (m, 1H), 2.74 (d, J=15.0Hz, 1H), 2.42 (d, J=3.6 Hz, 6H).

Example 1: Synthesis of(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(1)

Step 1: Synthesis of(2R,3S,5R)-5-(4-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

To a suspension of sodium hydride (60% dispersion in mineral oil, 0.272g, 6.79 mmol) in anhydrous acetonitrile (50 ml) under argon atmospherein a 250 ml three necked round-bottom flask, was added4-chloro-7H-pyrrolo[2,3-d]pyrimidine (0.948 g, 6.17 mmol) and themixture was stirred at ambient temperature for 30 minutes.(2R,3S,5R)-5-chloro-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (2.4 g, 6.17 mmol) was added in portions with stirring.The reaction mixture was heated to 50° C. and stirred for 2 hours. Thereaction progress was monitored by TLC & LCMS. Evaporation of thereaction mixture gave an oily residue, which was purified by silica-gelchromatography with ethyl acetate/petroleum ether (1:6, v/v) to give thetitle compound. 1H-NMR: (300 MHz, CDCl₃, ppm): δ 8.64 (s, 1H), 7.98 (d,J=8.1 Hz, 2H), 7.92 (d, J=8.1 Hz, 2H), 7.43 (d, J=3.6 Hz, 1H), 7.20-7.30(m, 4H), 6.82 (dd, J=5.7 Hz, J=8.1 Hz, 1H), 6.60 (d, J=3.9 Hz, 1H),4.60-4.76 (m, 3H), 2.86-2.96 (m, 1H), 2.74-2.82 (m, 1H), 2.43 (d, J=5.4Hz, 6H). LC-MS: (ES, m/z): 506.43 [M+H]⁺.

Step 2: Synthesis of(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

(2R,3S,5R)-5-(4-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (2.18 g, 4.31 mmol) was added to an 80 ml steel bomband it was cooled down to −40° C. To this was added isopropanolicammonia (saturated at −40° C., 60 ml). After the mixture was stirred at90° C. and for 15 hours, it was cooled down to room temperature andconcentrated under vacuum. The residue was purified by silica gel columnchromatography with dichloromethane/methanol (4/1) to give the titlecompound. 1H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.04 (s, 1H), 7.34 (d,J=3.6 Hz, 1H), 7.04 (br, 2H), 6.58 (d, J=3.6 Hz, 1H), 6.48 (dd, J=6.0Hz, J=8.0 Hz, 1H), 5.24 (d, J=3.6 Hz, 1H), 5.16 (t, J=4.2 Hz, 1H), 4.34(d, J=2.0 Hz, 1H), 3.82 (dd, J=4.0 Hz, J=6.4 Hz, 1H), 3.48-3.58 (m, 2H),2.48-2.54 (m, 1H), 2.13-2.17 (m, 1H).

Step 3: Synthesis of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine

(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(950 mg, 3.796 mmol) and imidazole (775.4 mg, 11.388 mmol) were addedinto a 25 mL round bottom flask under argon atmosphere. To the flask wasinjected anhydrous DMF (8 mL), followed by the addition oft-butyldimethylsilyl chloride (1716.4 mg, 11.388 mmol). After themixture was stirred at 25° C. for 3 hours, it was diluted with ethylacetate (40 mL), washed with water (20 mL×2), aqueous NaHCO₃ (saturated,20 mL×2) and brine (20 mL×2) respectively. The organic layer wascollected and dried over anhydrous Na₂SO₄, filtered and concentratedunder reduced pressure to give crude product. The crude product was thenpurified by silica gel chromatography with ethyl acetate/petroleum ether(35% to 42% ethyl acetate in petroleum ether) to give the titlecompound. ¹H-NMR: (300 MHz, CDCl₃, ppm): δ 8.32 (s, 1H), 7.32 (d, J=3.9Hz, 1H), 6.69 (t, J=6.6 Hz, 1H), 6.39 (d, J=3.6 Hz, 1H), 5.29 (br, 2H),4.56-4.61 (m, 1H), 3.96 (dd, J=3.5 Hz, J=7.0 Hz, 1H), 3.74-3.84 (m, 2H),2.42-2.51 (m, 1H), 2.30-2.38 (m, 1H), 0.92 (d, J=4.2 Hz, 18H), 0.08-0.1(m, 12H). LC-MS: (ES, m/z): 497.71 [M+H]⁺.

Step 4: Synthesis of((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol

To a stirred solution of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine(1.2 g, 2.506 mmol) in THF (24 mL), was added a pre-cooled solution oftrifluoroacetic acid/water (1/2, v/v, 9 mL) dropwise at 0° C. overperiod of 10 minutes. The resulting mixture was stirred at 0° C. for 4hours and then co-evaporated with toluene below 25° C. for three timesto give a syrup. The crude product was purified by silica gel columnchromatography with ethyl acetate/dichloromethane (1/1) to give thetitle compound. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.03 (s, 1H), 7.34(d, J=3.9 Hz, 1H), 7.03 (brs, 2H), 6.58 (d, J=3.6 Hz, 1H), 6.46 (dd,J=5.7 Hz, 1H), 5.19 (t, J=5.7 Hz, 1H), 4.51-4.53 (m, 1H), 3.79-3.83 (m,1H), 3.47-3.57 (m, 2H), 2.55-2.64 (m, 1H), 2.10-2.17 (m, 1H), 0.9 (s,9H), 0.11 (s, 6H).

Step 5: Synthesis of(2S,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde

To a stirred solution of((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol(100 mg, 0.274 mmol) in anhydrous acetonitrile (10 mL) under argonatmosphere in a 25 mL round-bottom flask, was added 2-Iodoxybenzoic acid(230 mg, 0.823 mmol). The resulting mixture was refluxed for 0.5 hoursand then cooled down to room temperature. The solids were filtered outand the filtrate was concentrated under reduced pressure to give thetitle compound, which was used to the next reaction step directlywithout further purification. LC-MS: (ES, m/z): 363.20 [M+H]⁺, 381.20[M+H+H₂O]⁺.

Step 6: Synthesis of((3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol

To a stirred solution of(2S,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde(100 mg, 0.276 mmol, crude) in 1,4-Dioxane (1 mL), was addedformaldehyde solution (0.3 mL, 4.00 mmol), followed by the addition ofsodium hydroxide solution (0.3 mL, 0.600 mmol, 2 M) dropwise in 1minute. The resulting mixture was stirred at 25° C. for 3 hours. Afterthe reaction completed, the reaction mixture was neutralized by additionof acetic acid, diluted with ethyl acetate and washed successively withwater, saturated aqueous NaHCO₃ and brine, dried over Na₂SO₄ andevaporated under reduced pressure. The residue was re-dissolved inanhydrous ethanol (2 mL) and added sodium borohydride (20.87 mg, 0.552mmol) in portions at 0° C. After stirring for 1 hour at 25° C., thereaction mixture was neutralized by addition of acetic acid, dilutedwith chloroform (20 mL), washed with water and brine. The organic layerwas dried over Na₂SO₄, and evaporated under reduced pressure. Theresidue was purified by preparative-TLC with dichloromethane/methanol(20/1) to give the title compound. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ8.03 (s, 1H), 7.37 (d, J=3.6 Hz, 1H), 7.02 (brs, 2H), 6.57 (d, J=3.6 Hz,1H), 6.50 (dd, J=5.7 Hz, J=8.1 Hz, 1H), 5.12 (dd, J=5.1 Hz, J=6.3 Hz,1H), 4.59-4.60 (m, 1H), 4.38 (dd, J=5.1 Hz, J=6.3 Hz, 1H), 3.46-3.61 (m,4H), 2.70-2.75 (m, 1H), 2.13-2.20 (m, 1H), 0.90 (s, 9H), 0.09 (s, 6H).LC-MS: (ES, m/z): 395.20 [M+H]⁺.

Step 7: Synthesis of(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

To a stirred solution of((3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol(100 mg, 0.253 mmol) in anhydrous acetonitrile (20 mL) under argonatmosphere, was added 2-Iodoxybenzoic acid (284 mg, 1.014 mmol). Theresulting mixture was stirred at 30° C. for 36 hours. LCMS indicatedthat little part of started diol-nucleoside was left, and targetcompound was the major product. The mixture was filtered, washed withdichloromethane. The filtrate was collected and concentrated underreduced pressure to give the title compound, which was used to the nextreaction step directly without further purification. LC-MS: (ES, m/z):393.28 [M+H]⁺.

Step 8: Synthesis of((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol

To a stirred solution of(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(100 mg, 0.248 mmol, crude) in anhydrous methanol (10 mL) under argonatmosphere, was added potassium carbonate (68.04 mg, 0.492 mmol). Themixture was cooled down to 0° C., then dimethyl(1-diazo-2-oxopropyl)phosphonate (94.56 mg, 0.492 mmol) was addeddropwise in 2 minutes. After the resulting mixture was stirred at 25° C.overnight, it was concentrated under reduced pressure. The residue waspurified by preparative-TLC (methanol/dichloromethane=1/15) to give thetitle compound. ¹H-NMR: (300 MHz, CDCl₃, ppm): δ 8.24 (s, 1H), 7.04 (d,J=3.6 Hz, 1H), 6.35 (d, J=3.6 Hz, 1H), 6.31 (dd, J=5.7 Hz, J=9.3 Hz,1H), 5.48 (br, 2H), 4.73 (d, J=4.2 Hz, 1H), 4.03 (d, J=12.6 Hz, 1H),3.80 (d, J=12.3 Hz, 1H), 3.13-3.23 (m, 1H), 2.58 (s, 1H), 2.22-2.28 (m,1H), 0.95 (s, 9H), 0.15 (d, J=7.2 Hz, 6H).

Step 9: Synthesis of(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol

To a stirred solution of((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(60 mg, 0.154 mmol) in anhydrous THF (2 mL) under argon atmosphere, wasadded 1M tetrabutylammonium fluoride THF solution (0.309 mL, 0.309 mmol)dropwise in 1 minute at ambient temperature. The resulting solution wasstirred at this temperature for 2 hours. The reaction progress wasmonitored by TLC. Upon the started nucleoside was all consumed, themixture was concentrated under reduced pressure. The residue waspurified by preparative-TLC (methanol/dichloromethane=1/9) to give crudetitle compound that was further purified by preparative-HPLC with thefollowing conditions: (1#-Pre-HPLC-011 (Waters)): Column, X-select CSHColumn, 19*150 mm, 5 um; mobile phase, water with 10 mmol ammoniumbicarbonate and acetonitrile (5% acetonitrile up to 20% in 7.5 min, upto 95% in 2 min); Detector, UV 254 & 220 nm to give compound 1 as asolid. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.05 (s, 1H), 7.31 (d, J=3.6Hz, 1H), 7.03 (brs, 2H), 6.58 (d, J=3.6 Hz, 1H), 6.50 (t, J=6.3 Hz, 1H),5.40-5.49 (m, 2H), 4.49 (dd, J=6.0 Hz, J=11.4 Hz, 1H), 3.51-3.66 (m,2H), 3.46 (s, 1H), 2.55-2.59 (m, 1H), 2.28-2.39 (m, 1H). LC-MS: (ES,m/z): 275.20 [M+H]⁺.

Example 2: Synthesis of(2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(2)

Step 1: Synthesis of 4-chloro-5-fluoro-7H-pyrrolo[2,3-d]pyrimidine

4-chloro-7H-pyrrolo[2,3-d]pyrimidine (5 g, 32.6 mmol) and SELECTFLUOR®(1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octanebis(tetrafluoroborate)) (17.30 g, 48.8 mmol) were placed in a 500 mLround-bottom flask under argon atmosphere. To the above was added dryacetonitrile (150 mL) and dry acetic acid (50 mL). The mixture washeated at 70° C. and stirred for 16 hours. After cooling down to roomtemperature, the solvents were removed under reduced pressure and theresidue was co-evaporated with toluene. The crude solid was dissolved ina mixture of dichloromethane/ethyl acetate (1:1) and filtered through apad of silica gel. The combined organic phases were evaporated underreduced pressure. The crude product was then purified by silica gelchromatography with dichloromethane/ethyl acetate (5:1) to give thetitle compound. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 12.48 (brs, 1H), 8.62(s, 1H), 7.71 (t, J=2.6 Hz, 1H). F-NMR: (376 MHz, d₆-DMSO, ppm):δ−170.76 (s, 1F). LC-MS: (ES, m/z): 172.00 [M+H]⁺.

Step 2: Synthesis of(2R,3S,5R)-5-(4-chloro-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

To a suspension of sodium hydride 60% dispersion in mineral oil (0.177g, 4.41 mmol) in anhydrous acetonitrile (40 mL) under argon atmosphere,was added 4-chloro-5-fluoro-7H-pyrrolo[2,3-d]pyrimidine (0.688 g, 4.01mmol) in portions and the mixture was stirred at ambient temperature for30 minutes. Then Intermediate A (1.56 g, 4.01 mmol) was added inportions. After the reaction mixture was heated to 50° C. and stirredfor 2 hours, the volatile was removed under reduced pressure, theresidue of was then purified by silica gel chromatography with ethylacetate/petroleum ether (1/1) to give the title compound. ¹H-NMR: (300MHz, CDCl₃, ppm): δ8.62-8.68 (m, 1H), 7.91-7.99 (m, 4H), 7.26-7.29 (m,4H), 7.16-7.18 (m, 2H), 6.84-6.88 (m, 1H), 5.74-5.76 (m, 1H), 4.60-4.74(m, 3H), 2.74-2.79 (m, 2H), 2.43-2.46 (m, 6H). LC-MS: (ES, m/z): 524.30[M+H]⁺.

Step 3: Synthesis of(2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

To an 80 mL steel bomb, was added(2R,3S,5R)-5-(4-chloro-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (2.0 g, 3.82 mmol). The medium was cooled to −40° C. Tothis was added ammonia saturated i-PrOH (60 mL). After the mixture washeated to 80° C. and stirred for 18 hours, the resulting mixture wasconcentrated under reduced pressure. The residue was purified by silicagel chromatography with dichloromethane/methanol (5/1) to give the titlecompound. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.06 (s, 1H), 7.33 (d,J=2.0 Hz, 1H), 6.99 (brs, 2H), 6.54 (t, J=6.0 Hz, 1H), 5.24 (d, J=4.4Hz, 1H), 4.99 (t, J=5.6 Hz, 1H), 4.30-4.33 (m, 1H), 3.78-3.81 (m, 1H),3.47-3.56 (m, 2H), 2.37-2.44 (m, 1H), 2.12-2.17 (m, 1H). F-NMR: (376MHz, d₆-DMSO, ppm): δ−167.49 (s, 1F).

Step 4: Synthesis of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-4-amine

(2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(538 mg, 2.006 mmol) and imidazole (819 mg, 12.03 mmol) were added intoa 25 mL round-bottom flask under argon atmosphere. To this was added dryDMF (5 mL), followed by the addition of tert-butylchlorodimethylsilane(1209 mg, 8.02 mmol) in portions. The resulting mixture was stirred at25° C. for 3 hours. The reaction progress was monitored by TLC and LCMS.After the reaction completed, the mixture was diluted with ethyl acetate(40 mL), washed with water (20 mL×2), saturated aqueous NaHCO₃ (20 mL×2)and brine (20 mL×2) respectively. The organic layer was collected, driedover anhydrous Na₂SO₄ and concentrated under reduced pressure. The crudeproduct was then purified by silica gel chromatography with ethylacetate/petroleum ether (28% to 41% ethyl acetate in petroleum ether) togive the title compound. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.07 (s,1H), 7.27 (s, 1H), 6.99 (brs, 2H), 6.54 (t, J=6.0 Hz, 1H), 4.49 (s, 1H),3.60-3.78 (m, 3H), 2.51-2.53 (m, 1H), 2.16-2.20 (m, 1H), 0.88 (d, J=4.2Hz, 18H), 0.11 (s, 6H), 0.04 (s, 6H). LC-MS: (ES, m/z): 497.71 [M+H]⁺.

Step 5: Synthesis of((2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol

To a stirred solution of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-4-amine(900 mg, 1.812 mmol) in THF (12 mL) was added aqueous trifluoroaceticacid (trifluoroacetic acid/water=1/1, v/v, 6 mL) dropwise with stirringat 0° C. in 10 minutes. The resulting mixture was stirred at 0° C. Thereaction progress was monitored by TLC. After the reaction wascompleted, the resulting mixture was co-evaporated with toluene (50mL×3) under vacuum while the temperature maintained below 25° C. toremove the volatiles. The residue was purified by silica gelchromatography with ethyl acetate/petroleum ether (52% to 58% ethylacetate in petroleum ether) to give the title compound. ¹H-NMR: (300MHz, d₆-DMSO, ppm): δ8.07 (s, 1H), 7.34 (s, 1H), 6.99 (brs, 2H), 6.53(t, J=6.9 Hz, 1H), 5.04 (t, J=5.6 Hz, 1H), 4.47-4.51 (m, 1H), 3.76-3.79(m, 1H), 3.44-3.57 (m, 2H), 2.45-2.51 (m, 1H), 2.11-2.16 (m, 1H), 0.90(s, 9H), 0.11 (s, 6H). LC-MS: (ES, m/z): 383.26 [M+H]⁺.

Step 6: Synthesis of(2S,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde

To a stirred solution of((2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol(360 mg, 0.941 mmol) in anhydrous acetonitrile (12 mL) under argon, wasadded 2-iodoxybenzoic acid (791 mg, 2.82 mmol). The resulting mixturewas refluxed for 35 minutes. The reaction was cooled down to roomtemperature, and the solids were filtered out. The filtration wascollected and then concentrated under vacuum to give the title compound,which was used to the next reaction step directly without furtherpurification.

Step 7: Synthesis of((3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol

To a stirred solution of(2S,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde(400 mg, 1.051 mmol, crude) in 1,4-dioxane (4 mL), was addedformaldehyde solution (1.2 mL, 16.01 mmol), followed by the addition ofsodium hydroxide solution (1.2 mL, 2 M, 2.400 mmol) dropwise over 5minutes. The resulting mixture was stirred at 25° C. for 3 hours, andthen the reaction mixture was neutralized by addition of acetic acid.The resulting mixture was diluted with ethyl acetate, washedsuccessively with water, saturated aqueous NaHCO₃ and brine. The organicphase was dried over Na₂SO₄ and evaporated under reduced pressure. Theresidue was dissolved in ethanol (10 mL) and sodium borohydride wasadded (80 mg, 2.103 mmol) in portions at 0° C. After stirring for 1 hourat 25° C., the reaction mixture was neutralized by addition of aceticacid and then diluted with chloroform and washed successively with waterand brine. The organic layer was dried over Na₂SO₄ and evaporated underreduced pressure. The residue was purified by silica gel chromatographywith dichloromethane/methanol (30/1) to give the title compound. ¹H-NMR:(300 MHz, d₆-DMSO, ppm): δ 8.06 (s, 1H), 7.36 (s, 1H), 6.99 (brs, 2H),6.57 (t, J=3.6 Hz, 1H), 4.99 (t, J=4.8 Hz, 1H), 4.55-4.59 (m, 1H), 4.39(t, J=5.1 Hz, 1H), 3.45-3.55 (m, 4H), 2.57-2.65 (m, 1H), 2.17-2.20 (m,1H), 0.90 (s, 9H), 0.09 (s, 6H).

Step 8: Synthesis of(2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

To a stirred solution of((3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol(120 mg, 0.291 mmol) in anhydrous acetonitrile (8 mL) under argonatmosphere, was added 2-iodoxybenzoic acid (326 mg, 1.164 mmol). Theresulting mixture was stirred at 30° C. for 24 hours and then filteredand washed with dichloromethane. The filtrate was collected andconcentrated under reduced pressure to give the title compound, whichwas used in the next reaction step directly without furtherpurification. LC-MS: (ES, m/z): 411.43 [M+H]⁺.

Step 9: Synthesis of((2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol

To a stirred solution of(2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(110 mg, 0.268 mmol, crude) in anhydrous methanol (8 mL) under argon,was added potassium carbonate (111 mg, 0.804 mmol). The mixture wascooled down to 0° C., then dimethyl (1-diazo-2-oxopropyl)phosphonate(154 mg, 0.804 mmol) was added dropwise over 1 minute. After the mixturewas stirred at 25° C. overnight, the resulting mixture was concentratedunder vacuum, and then purified by preparative-TLC(methanol/dichloromethane=1/15) to give the title compound. ¹H-NMR: (300MHz, d₆-DMSO, ppm): δ 8.07 (s, 1H), 7.34 (s, 1H), 7.03 (br, 2H), 6.56(t, J=6.3 Hz, 1H), 5.43 (t, J=6.0 Hz, 1H), 4.61 (t, J=5.4 Hz, 1H),3.58-3.67 (m, 1H), 3.49-3.53 (m, 1H), 3.47 (s, 1H), 2.52-2.61 (m, 1H),2.23-2.31 (m, 1H), 0.91 (s, 9H), 0.11 (d, J=2.4 Hz, 6H). LC-MS: (ES,m/z): 407.30 [M+H]⁺.

Step 10: Synthesis of(2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol

To a stirred solution of((2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(40 mg, 0.098 mmol) in anhydrous THF (2 mL) under argon atmosphere, wasadded TBAF/THF solution (0.118 mL, 0.118 mmol) dropwise with stirringover 1 minute at room temperature and the resulting solution was stirredat this temperature for 2 hours. After the reaction completed, theresulting mixture was concentrated under vacuum, and the residue waspurified by preparative-TLC (methanol/dichloromethane=1/10) to givecrude product (28 mg). The crude product was further purified bypreparative-HPLC with the following conditions: (1#-Pre-HPLC-011(Waters)): Column, X-select CSH Column, 19*150 mm, 5 um; mobile phase,water with 10 mmol ammonium bicarbonate and acetonitrile (5%acetonitrile up to 35% in 7.5 min, up to 95% in 2 min); Detector, UV 254& 220 nm. The product-containing fractions were collected andlyophilized to give compound 2 as a solid. ¹H-NMR: (400 MHz, d₆-DMSO,ppm): δ8.07 (s, 1H), 7.30 (d, J=1.6 Hz, 1H), 7.02 (br, 2H), 6.55 (t,J=5.8 Hz, 1H), 6.05 (br, 1H), 5.31-5.45 (m, 1H), 4.46 (t, J=6.6 Hz, 1H),3.58 (dd, J=11.8 Hz, J=29.4 Hz, 2H), 3.47 (s, 1H), 2.44-2.51 (m, 1H),2.29-2.36 (m, 1H). F-NMR: (376 MHz, d₆-DMSO, ppm): δ−167.23 (s, 1F).LC-MS: (ES, m/z): 293.10 [M+H]⁺, 315.10 [M+Na]⁺.

Example 3: Synthesis of(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(3)

Step 1: 5-bromo-4-chloro-7H-pyrrolo[2,3-d]pyrimidine

4-chloro-7H-pyrrolo[2,3-d]pyrimidine (1 g, 6.51 mmol) was suspended indry DCM (20 mL) followed by the addition of NBS (N-bromosuccinimide)(1.275 g, 7.16 mmol) at ambient temperature under argon atmosphere. Themixture was heated to reflux and stirred 16 hours. Upon the starteddeaza-pyrimidine was all consumed, the mixture was cooled to ambienttemperature and maintained for 30 min. The precipitated was collected byfiltration, washed with DCM (2×20 mL), dried under vacuum to give thetitle compound. LC-MS: (ES, m/z): 233.90 [M+H]⁺. ¹H-NMR: (300 MHz,d₆-DMSO, ppm): δ 12.98 (brs, 1H), 8.64 (s, 1H), 7.96 (s, 1H).

Step 2: Synthesis of 4-chloro-5-methyl-7H-pyrrolo[2,3-d]pyrimidine

5-bromo-4-chloro-7H-pyrrolo[2,3-d]pyrimidine (232 mg, 0.998 mmol) wasdissolved in dry THF (10 mL) and cooled to −78° C. under argonatmosphere. To this was added n-butyllithium hexanes solution (2.5 M,0.88 mL, 2.196 mmol) dropwise with stirring in 5 minutes. The mixturewas stirred for about 40 minutes followed by the addition of iodomethane(212 mg, 1.497 mmol). The solution was then warmed slowly to roomtemperature in 2 hours. Water (2 mL) was added to quench the reaction.The volatile was removed in vacuo below 40° C. to yield a slurry. Theslurry was re-dissolved in EtOAc (50 mL) and washed with water (2×15 mL)and brine (20 mL). The organic layer was collected, dried over anhydrousNa₂SO₄, filtered and the filtrate was concentrated in vacuo to yield apowder that was re-crystallized from MeOH to afford the title compound.LC-MS: (ES, m/z): 168.00 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ12.22 (brs, 1H), 8.51 (s, 1H), 7.43 (s, 1H), 2.41 (d, J=0.90 Hz, 1H).

Step 3: Synthesis of(2R,3S,5R)-5-(4-chloro-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

To a stirred suspension of sodium hydride (60% dispersion in oil, 0.453g, 11.32 mmol) in anhydrous ACN (50 mL) was added4-chloro-5-methyl-7H-pyrrolo[2,3-d]pyrimidine (1.724 g, 10.29 mmol) inportions under argon atmosphere and the mixture was stirred at 25° C.for 30 minutes. To the resulted clear solution was added Intermediate A(4.0 g, 10.29 mmol) portionwise at 25° C. The resulting mixture washeated to 50° C. and stirred for 3 hours. The reaction progress wasmonitored by TLC. The mixture was concentrated under vacuum gave asolid, which was purified by silica-gel column chromatography usingethyl acetate/petrol ether (1:6, v/v) to give the title compound. LC-MS:(ES, m/z): 520.25 [M+H]⁺. ¹H-NMR: (300 MHz, CDCl₃, ppm): δ 8.55 (s, 1H),7.90-7.99 (m, 4H), 7.20-7.30 (m, 4H), 7.11 (s, 1H), 6.81 (dd, J=6.0 Hz,J=8.4 Hz, 1H), 5.76 (dd, J=1.5 Hz, J=3.6 Hz, 1H), 4.73-4.79 (m, 1H),4.54-4.64 (m, 2H), 2.79-2.88 (m, 1H), 2.68-2.75 (m, 1H), 2.43 (d, J=3.0Hz, 6H), 2.33 (d, J=0.9 Hz, 3H).

Step 4: Synthesis of(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

To a 150 mL steel bomb was placed(2R,3S,5R)-5-(4-chloro-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (4.5 g, 7.79 mmol). The medium was cooled to −40° C. Tothis was added 2-propanolic ammonia (i-PrOH/Liquid NH₃=1/1, v/v, 120mL). The bomb was sealed and the mixture was heated to 90° C. andstirred for 40 hours. Upon the reaction was complete, the mixture wascooled to 0° C. and concentrated under vacuum. The residue was purifiedby silica gel column chromatography using DCM/MeOH (4/1) to give thetitle compound. LC-MS: (ES, m/z): 265.10 [M+H]⁺. ¹H-NMR: (300 MHz,d₆-DMSO, ppm): δ 8.00 (s, 1H), 7.08 (s, 1H), 6.58 (brs, 2H), 6.45 (dd,J=6.0 Hz, J=8.1 Hz, 1H), 5.21 (d, J=3.3 Hz, 1H), 5.05 (t, J=5.1 Hz, 1H),4.32-4.36 (m, 1H), 3.78 (d, J=2.1 Hz, 1H), 3.44-3.57 (m, 2H), 2.39-2.51(m, 1H), 2.33 (s, 3H), 2.06-2.13 (m, 3H).

Step 5: Synthesis of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-4-amine

To a stirred solution of(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(1.7 g, 6.43 mmol) and 1H-imidazole (1.752 g, 25.7 mmol) in dry DMF (10mL) was added tert-butylchlorodimethylsilane (2.91 g, 19.30 mmol) withstirring at 25° C. under argon atmosphere. The resulting mixture wasstirred at 25° C. for 3 hours and then diluted with ethyl acetate (100mL), washed with water (2×30 mL), aqueous NaHCO₃ (saturated, 2×30 mL)and brine (30 mL) respectively. The organic layer was collected anddried over anhydrous Na2SO4, filtered and concentrated under vacuum togive crude product. The crude product was then purified by silica gelcolumn chromatography using ethyl acetate/petroleum ether (28% to 41% EAin PE) to give the title compound. LC-MS: (ES, m/z): 493.30 [M+H]⁺.¹H-NMR: (300 MHz, CDCl₃, ppm): δ 8.24 (s, 1H), 7.02 (s, 1H), 6.67 (dd,J=6.3 Hz, J=7.2 Hz, 1H), 5.37 (br, 2H), 4.54-4.57 (m, 1H), 3.94 (dd,J=3.3 Hz, J=6.3 Hz, 1H), 3.72-3.82 (m, 2H), 2.37-2.46 (m, 4H), 2.25-2.32(m, 1H), 0.91 (2s, 18H), 0.10 (s, 12H).

Step 6: Synthesis of((2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-(tert-butyldimethylsilyl)tetrahydrofuran-2-yl)methanol

To a stirred solution of7-((2R,4S,5R)-4-(tert-butyldimethylsilyl)-5-((tert-butyldimethylsilyl)methyl)tetrahydrofuran-2-yl)-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-4-amine(2.5 g, 5.07 mmol) in THF (30 mL) was added a pre-cooled solution oftrifluoroacetic acid/water (1/1, v/v, 15 mL) dropwise with stirring at0° C. in 10 minutes. The resulting mixture was stirred at 0° C. for 3hours. The reaction progress was monitored by TLC. The resultingsolution was co-evaporated with toluene (3×100 mL) while maintaining theinner temperature below 25° C. The resulting crude product was thenpurified by silica gel column chromatography using ethylacetate/petroleum ether (50% to 58% EA in PE) to give the titlecompound. LC-MS: (ES, m/z): 493.30 [M+H]⁺. ¹H-NMR: (300 MHz, CD₃OD,ppm): δ 8.18 (s, 1H), 7.41 (s, 1H), 6.59 (dd, J=6.0 Hz, J=7.8 Hz, 1H),4.56-4.60 (m, 1H), 3.93 (dd, J=3.9 Hz, J=6.6 Hz, 1H), 3.65-3.70 (m, 2H),2.45-2.54 (m, 1H), 2.42 (d, J=0.9 Hz, 3H), 2.23-2.31 (m, 1H), 0.91 (s,9H), 0.11 (s, 6H).

Step 7: Synthesis of(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-(tert-butyldimethylsilyl)tetrahydrofuran-2-carbaldehyde

To a stirred suspension of((2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-(tert-butyldimethylsilyl)tetrahydrofuran-2-yl)methanol(600 mg, 1.585 mmol) in anhydrous ACN (12 mL) was added IBX (888 mg,3.17 mmol) under argon atmosphere. The mixture was heated to reflux andstirred for 55 minutes. The reaction progress was monitored by LCMS. Themixture was cooled to room temperature, and the solids were filteredout. The filtration was collected and then concentrated under vacuum togive the title compound, which was used to the next reaction stepdirectly without further purification. LC-MS: (ES, m/z): 377.15 [M+H]⁺,409.15 [M+H+MeOH]⁺.

Step 8: Synthesis of((3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-(tert-butyldimethylsilyl)tetrahydrofuran-2,2-diyl)dimethanol

To a stirred solution of(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-(tert-butyldimethylsilyl)tetrahydrofuran-2-carbaldehyde(420 mg, crude) in 1,4-Dioxane (12 mL) and water (3 mL) in a 50 mLround-bottom flask, was added aqueous formaldehyde (37% w/w, 6 mL)followed by the addition of sodium hydroxide solution (2 N, 6 mL, 0.12mmol) dropwise in 2 minutes. The resulting mixture was stirred at 25° C.for 3 hours. Upon the started nucleoside-aldehyde was all consumed, thereaction mixture was neutralized by the addition of AcOH (about 0.8 mL).The resulting mixture was diluted with AcOEt (50 mL) and washedsuccessively with water (30 mL), saturated aqueous NaHCO₃ (20 mL) andbrine (20 mL). The organic layer was dried over anhydrous Na₂SO₄,filtered and concentrated under vacuum. The residue was re-dissolved inanhydrous EtOH (8 mL) and added sodium borohydride (84.4 mg, 2.23 mmol)in portions at 0° C. After stirring for 1 hour at 25° C., the reactionmixture was neutralized by addition of AcOH. The mixture wasconcentrated under vacuum, partitioned between CHCl₃ (50 mL) and water(30 mL). The aqueous layer was re-extracted with CHCl₃ (2×20 mL). Thecombined organic layer was washed successively with water and brine,dried over anhydrous Na₂SO₄, filtered and concentrated under vacuum. Theresidue was purified by purified by silica gel column chromatographyusing dichloromethane/methanol (5.5% MeOH in DCM) to give the titlecompound. LC-MS: (ES, m/z): 409.35 [M+H]⁺, 431.35 [M+Na]⁺. ¹H-NMR: (300MHz, d₆-DMSO, ppm): δ 8.00 (s, 1H), 7.11 (s, 1H), 6.56 (br, 2H), 6.48(dd, J=6.0 Hz, J=8.4 Hz, 1H), 6.45-6.47 (m, 1H), 5.02 (t, J=5.5 Hz, 1H),4.58 (t, J=2.7 Hz, 1H), 4.35 (dd, J=4.5 Hz, J=6.3 Hz, 1H), 3.42-3.60 (m,4H), 2.58-2.63 (m, 1H), 2.34 (s, 3H), 2.09-2.16 (m, 1H), 0.90 (s, 9H),0.09 (s, 6H).

Step 9: Synthesis of(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

((3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol (140 mg, 0.343 mmol) was suspendedin dry ACN (15 mL) under argon atmosphere followed by the addition of2-iodylbenzoic acid (240 mg, 0.857 mmol). The mixture was stirred at 30°C. for 20 hours. The solid was filtered out, washed with CHCl₃ (2×20mL). The combined filtrate was concentrated under vacuum to afford thetitle compound, which was used to the next reaction step directlywithout further purification. LC-MS: (ES, m/z): 407.25 [M+H]⁺.

Step 10: Synthesis of((2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol

To a stirred solution of(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(120 mg, ˜0.236 mmol, crude) in dry MeOH (15 mL) was added K₂CO₃ (82 mg,0.590 mmol) at 0° C. under argon atmosphere, followed by the addition ofa solution of dimethyl (1-diazo-2-oxopropyl)phosphonate (91 mg, 0.472mmol) in MeOH (2 mL) dropwise with stirring at 0° C. in 2 minutes. Theresulting mixture was gradually warmed to 25° C. and stirred for 16hours. The mixture was concentrated under vacuum. The residue waspurified by flash silica gel column chromatography using ethylacetate/petroleum ether (30%-50% EA in PE) to afford the title compound.LC-MS: (ES, m/z): 403.25 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.01(s, 1H), 7.07 (s, 1H), 6.60 (br, 2H), 6.49 (dd, J=6.0 Hz, J=7.2 Hz, 1H),5.48 (t, J=5.7 Hz, 1H), 4.62 (t, J=5.7 Hz, 1H), 3.57-3.68 (m, 1H),3.48-3.52 (m, 1H), 3.45 (s, 1H), 2.49-2.62 (m, 1H), 2.33 (s, 3H),2.21-2.31 (m, 1H), 0.91 (s, 9H), 0.12 (d, J=6.0 Hz, 6H).

Step 11: Synthesis of(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(3)

To a stirred solution of((2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(27 mg, 0.067 mmol) in dry THF (1 mL) was added tetra-butylammoniumfluoride THF solution (1.0 M, 0.067 mL, 0.067 mmol) dropwise withstirring at 0° C. The resulting mixture was stirred at 25° C. for 30minutes. The reaction progress was monitored by TLC. The resultingsolution was concentrated under vacuum. The crude product was purifiedby preparative-HPLC with the following conditions (1#-Pre-HPLC-011(Waters)): Column, XBridge™ C18 Column, 19*150 mm, 5 um; mobile phase,water with 10 mmol ammonium bicarbonate and acetonitrile (30%acetonitrile up to 70% in 10 min, up to 95% in 2 min, down to 5% in 1.5min); Flow rate: 20 mL/min; Detector, UV 254&220 nm. Theproduct-containing fractions were collected and lyophilized to give thetitle compound. LC-MS: (ES, m/z): 289.05 [M+H]⁺. ¹H-NMR: (300 MHz,d₆-DMSO, ppm): δ8.00 (s, 1H), 7.06 (s, 1H), 6.58 (br, 2H), 6.48 (t,J=6.60 Hz, 1H), 5.45 (d, J=5.1 Hz, 1H), 5.38 (t, J=6.0 Hz, 1H), 4.46 (q,J=5.4 Hz, 1H), 3.50-3.64 (m, 2H), 3.44 (s, 1H), 2.44-2.54 (m, 1H), 2.33(s, 3H), 2.24-2.32 (m, 1H).

Example 4: Synthesis of(2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(4)

Step 1: Synthesis of(2R,3S,5R)-5-(2,4-dichloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

To a stirred suspension of sodium hydride (60% dispersion in mineraloil, 0.509 g, 12.73 mmol) in anhydrous acetonitrile (125 mL) was added2,4-dichloro-7H-pyrrolo[2,3-d]pyrimidine (2.176 g, 11.57 mmol) inportions under argon atmosphere and the mixture was stirred at ambienttemperature for 30 minutes. To the above clear solution was addedIntermediate A (4.5 g, 11.57 mmol) batch wise with stirring. Thereaction mixture was allowed to stir at ambient temperature for 2 hours.The reaction progress was monitored by TLC. Evaporation of the reactionmixture gave an oily residue, which was purified by silica-gel columnchromatography using ethyl acetate/petroleum ether (1/6, v/v) to givethe title compound. LC-MS: (ES, m/z): 540.20 [M+H]⁺. ¹H-NMR: (400 MHz,CDCl₃, ppm): δ 8.01 (d, J=8.0 Hz, 2H), 7.93 (d, J=8.0 Hz, 2H), 7.43 (d,J=3.6 Hz, 1H), 7.22-7.37 (m, 4H), 6.80 (dd, J=6.0 Hz, J=8.0 Hz, 1H),6.61 (d, J=4.0 Hz, 1H), 5.76 (t, J=2.8 Hz, 1H), 4.76 (dd, J=3.6 Hz,J=12.0 Hz, 1H), 4.63-4.69 (m, 2H), 2.76-2.86 (m, 2H), 2.47, 2.45 (2s,6H).

Step 2: Synthesis of(2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

To a 250 mL steel bomb was added(2R,3S,5R)-5-(2,4-dichloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (5 g, 9.25 mmol). The medium was cooled to −40° C. Tothis was added isopropanolic ammonia (isopropanol/liquid ammonia=1/3,v/v, 150 mL). The medium was sealed, heated to 90° C. and stirred for 16hours. The resulting mixture was cooled to room temperature andconcentrated under vacuum. The residue was re-dissolved in MeOH (100mL), followed by the addition of sodium methoxide MeOH solution (1.0 M,16.89 mL, 16.89 mmol) dropwise at 0° C. The resulting mixture was warmedto 25° C. and stirred for 2 hours. After the reaction achieved tocomplete, the mixture was neutralized by the addition of acetic acid(0.01 mL) and concentrated under vacuum. The residue was suspended inDCM/MeOH (v/v, 100/1, 150 mL). After stirring for 20 minutes, a solidwas precipitated. The solid was collected by filtration, washed with DCMand dried in vacuo to give the title compound. LC-MS: (ES, m/z): 285.20[M+H]⁺. ¹H-NMR: (400 MHz, CD₃OD, ppm): δ 7.31 (d, J=2.8 Hz, 1H), 6.58(d, J=2.8 Hz, 1H), 6.45 (t, J=6.8 Hz, 1H), 4.52-4.53 (m, 1H), 3.98-4.01(m, 1H), 3.81 (dd, J=2.4 Hz, J=12.0 Hz, 1H), 3.73 (dd, J=3.2 Hz, J=12.0Hz, 1H), 2.63-2.70 (m, 1H), 2.29-2.34 (m, 1H).

Step 3: Synthesis of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-4-amine

To a stirred solution of(2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(3.2 g, 6.74 mmol) and imidazole (1.836 g, 27.0 mmol) in dry DMF (10 mL)under argon atmosphere was added TBS-Cl (3.05 g, 20.23 mmol) at ambienttemperature. The resulting mixture was stirred overnight. The reactionmixture was diluted with ethyl acetate (100 mL), washed with water (2×20mL), aqueous NaHCO₃ (saturated, 2×20 mL) and brine (2×20 mL)successively. The organic layer was dried over anhydrous Na₂SO₄,filtered and concentrated under vacuum. The residue was purified bysilica gel column chromatography using ethyl acetate/petroleum ether(35% to 42% EA in PE) to give the title compound. LC-MS: (ES, m/z):513.20 [M+H]⁺. ¹H-NMR: (400 MHz, CDCl₃, ppm): δ7.32 (s, 1H), 6.61 (t,J=6.8 Hz, 1H), 6.38 (s, 1H), 5.44 (br, 2H), 4.59-4.61 (m, 1H), 3.91-3.99(m, 1H), 3.77-3.88 (m, 2H), 2.44-2.51 (m, 1H), 2.34-2.37 (m, 1H),0.93-0.95 (m, 18H), 0.11-0.12 (m, 12H). ¹H-NMR: (400 MHz, CD₃OD, ppm): δ7.31 (d, J=2.8 Hz, 1H), 6.58 (d, J=2.8 Hz, 1H), 6.45 (t, J=6.8 Hz, 1H),4.52-4.53 (m, 1H), 3.98-4.01 (m, 1H), 3.81 (dd, J=2.4 Hz, J=12.0 Hz,1H), 3.73 (dd, J=3.2 Hz, J=12.0 Hz, 1H), 2.63-2.70 (m, 1H), 2.29-2.34(m, 1H).

Step 4: Synthesis of((2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol

To a stirred solution of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-4-amine(2.3 g, 4.48 mmol) in THF (40 mL) was added a pre-cooled solution oftrifluoroacetic acid/water (v/v, 1/1, 20 mL) dropwise with stirring at0° C. in 10 minutes. The resulting mixture was stirred for 2 hours at 0°C. The reaction progress was monitored by TLC. The resulting solutionwas co-evaporated with toluene (3×60 mL) while maintain the innertemperature below 25° C. give a pink syrup. The residue was purified bysilica gel column chromatography using ethyl acetate/dichloromethane(1/1) to give the title compound. LC-MS: (ES, m/z): 399.20 [M+H]⁺.¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 7.53 (br, 2H), 7.35 (d, J=3.2 Hz,1H), 6.60 (d, J=3.2 Hz, 1H), 6.35 (t, J=6.8 Hz, 1H), 4.95 (t, J=5.4 Hz,1H), 4.51-4.54 (m, 1H), 3.73-3.79 (m, 1H), 3.46-3.55 (m, 2H), 2.54-2.59(m, 1H), 2.16-2.20 (m, 1H), 0.90 (s, 9H), 0.11 (s, 6H). ¹H-NMR: (400MHz, d₆-DMSO, ppm): δ 7.53 (br, 2H), 7.35 (d, J=3.2 Hz, 1H), 6.60 (d,J=3.2 Hz, 1H), 6.35 (t, J=6.8 Hz, 1H), 4.95 (t, J=5.4 Hz, 1H), 4.51-4.54(m, 1H), 3.73-3.79 (m, 1H), 3.46-3.55 (m, 2H), 2.54-2.59 (m, 1H),2.16-2.20 (m, 1H), 0.90 (s, 9H), 0.11 (s, 6H).

Step 5: Synthesis of(2S,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde

To a stirred solution of((2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol(600 mg, 1.504 mmol) in anhydrous DMSO (3 mL) and acetonitrile (15 mL)under argon atmosphere was added IBX (632 mg, 2.256 mmol). The mixturewas stirred at ambient temperature for 2.5 hours. The reaction mixturewas diluted with ethyl acetate (20 mL), washed with brine (2×10 mL),dried over anhydrous sodium sulfate and filtered. The filtrate wasconcentrated under vacuum to afford the title compound, which was usedto the next step directly without further purification. LC-MS: (ES,m/z): 415.40 [M+H₂O]⁺.

Step 6: Synthesis of((3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol

To a stirred solution of(2S,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde(700 mg, crude) in 1,4-dioxane (28 mL) and water (7 mL) was addedformaldehyde solution (7 mL, 93 mmol), followed by addition a aqueoussolution of sodium hydroxide (7 mL, 2 N, 14.00 mmol) dropwise in 5minutes. The resulting mixture was stirred at 25° C. for 3 hours. Uponthe started nucleoside-aldehyde was all consumed, the reaction mixturewas neutralized by the addition of acetic acid (0.5 mL). The mixture wasdiluted with ethyl acetate (100 mL) and washed successively with water(2×20 mL), saturated aqueous NaHCO₃ (20 mL) and brine (20 mL). Theorganic layer was dried over Na₂SO₄, filtered and concentrated undervacuum. The residue was re-dissolved in anhydrous EtOH (4 mL) and addedsodium borohydride (133 mg, 3.53 mmol) under argon atmosphere inportions at 0° C. After stirring for 1 hour at 25° C., the mixture wasneutralized by the addition of acetic acid (1.0 mL). The mixture wasconcentrated under vacuum. The residue was diluted with CHCl₃ (100 mL)and washed successively with water (2×20 mL) and brine (1×20 mL). Theorganic layer was dried over Na₂SO₄, filtered and concentrated undervacuum. The residue was purified by silica gel column chromatographyusing DCM/MeOH (30/1) to give the title compound. LC-MS: (ES, m/z):429.30 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 7.51 (br, 2H), 7.38(d, J=3.9 Hz, 1H), 6.60 (d, J=3.6 Hz, 1H), 6.40 (t, J=6.9 Hz, 1H), 4.88(t, J=5.5 Hz, 1H), 4.62 (dd, J=3.3 Hz, J=5.5 Hz, 1H), 4.39 (t, J=5.7 Hz,1H), 3.43-3.63 (m, 4H), 2.61-2.70 (m, 1H), 2.21-2.29 (m, 1H), 0.90 (s,9H), 0.10 (s, 6H).

Step 7: Synthesis of(2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

To a stirred solution of((3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol(150 mg, 0.350 mmol) in dry acetonitrile (15 mL) was added IBX (294 mg,1.049 mmol) under argon atmosphere. The resulting mixture was stirred at30° C. for 2 hours. The mixture was filtered, washed with CHCl3 (3×15mL). The filtrate was collected and then concentrated under vacuum togive the title compound, which was used to the next step directlywithout further purification. LC-MS: (ES, m/z): 427.30 [M+H]⁺.

Step 8: Synthesis of((2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol

(2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(200 mg, 0.468 mmol) was dissolved in anhydrous MeOH (9 mL) followed bythe addition of potassium carbonate (162 mg, 1.171 mmol) at 0° C. underargon atmosphere. To the suspension was added a solution of dimethyl(1-diazo-2-oxopropyl)phosphonate (180 mg, 0.937 mmol) in MeOH (1 mL)dropwise with stirring in 1 minute. The resulting mixture was warmed to30° C. and stirred for 16 hours. The reaction mixture was concentratedunder vacuum. The residue was partitioned between ethyl acetate (30 mL)and water (10 mL). The organic layer was collected, washed with brine(2×10 mL), dried over anhydrous Na₂SO₄, filtered and concentrated undervacuum. The residue was then purified by preparative-TLC (MeOH/DCM=1/15)to afford the title compound. LC-MS: (ES, m/z): 423.60 [M+H]⁺. ¹H-NMR:(400 MHz, d₆-DMSO, ppm): δ 7.55 (br, 2H), 7.34 (d, J=3.6 Hz, 1H), 6.61(d, J=3.6 Hz, 1H), 6.38 (t, J=6.4 Hz, 1H), 5.32 (t, J=6.0 Hz, 1H), 4.67(t, J=6.0 Hz, 1H), 3.58-3.61 (m, 1H), 3.48-3.52 (m, 1H), 3.47 (s, 1H),2.60-2.63 (m, 1H), 2.31-2.35 (m, 1H), 0.91 (s, 9H), 0.11 (d, J=3.6 Hz,6H).

Step 9: Synthesis of(2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol

To a stirred solution of((2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(60 mg, 0.142 mmol) in THF (1 mL) was added TBAF THF solution (1 M, 0.28mL, 0.284 mmol) dropwise with stirring at ambient temperature. Theresulting solution was stirred at ambient temperature for 2 hours. Themixture was concentrated under vacuum. The residue was then purified byPrep-HPLC with the following conditions (1#-Pre-HPLC-011 (Waters)):Column, SunFire Prep C18 OBD Column, 5 um, 19*150 mm; mobile phase,water (with 10 mmol ammonium bicarbonate) and acetonitrile (8%acetonitrile up to 40% in 6 min, up to 95% in 1.5 min, down to 5% in 1min); Detector, uv 254&220 nm. The product-containing fractions werecollected and lyophilized to give compound 4 as a solid. LC-MS: (ES,m/z): 309.00 [M+H]⁺. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 7.54 (br, 2H),7.33 (d, J=4.0 Hz, 1H), 6.60 (d, J=3.6 Hz, 1H), 6.41 (t, J=6.4 Hz, 1H),5.52-5.53 (m, 1H), 5.26 (t, J=6.0 Hz, 1H), 4.47-4.48 (m, 1H), 3.61 (dd,J=5.2 Hz, J=11.6 Hz, 1H), 3.53 (dd, J=6.2 Hz, J=11.8 Hz, 1H), 3.48 (s,1H), 2.41-2.50 (m, 1H), 2.32-2.38 (m, 1H)

Example 5: Synthesis of(2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(5)

Step 1: Synthesis of(2R,3S,5S)-5-(5-bromo-4-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

Sodium hydride (0.479 g, 11.98 mmol) was added to a stirred solution of5-bromo-4-chloro-7H-pyrrolo[2,3-d]pyrimidine (2.32 g, 9.98 mmol,synthesis described in Example 3, Step 1) in acetonitrile (30 mL). Theresulting mixture was stirred for 30 minutes at 0° C., and then(2R,3S,5R)-5-chloro-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (4.27 g, 10.98 mmol) was added. After the resultingmixture was stirred at room temperature for 1 hour, it was diluted with200 mL of ethyl acetate, washed with saturated aqueous sodiumbicarbonate (60 mL) and saturated aqueous sodium chloride (60 mL), driedover anhydrous sodium sulfate, and concentrated under vacuum. Theresidue was purified by silica gel column chromatography with petroleumetherethyl acetate (1:2) to give the title compound: ¹H-NMR (300 MHz,DMSO) δ 8.65 (s, 1H), 8.22 (s, 1H), 7.96 (d, J=8.4 Hz, 2H), 7.84 (d,J=8.1 Hz, 2H), 7.24-7.39 (m, 4H), 6.76-6.79 (m, 1H), 5.74-5.76 (m, 1H),4.51-4.68 (m, 3H), 3.05-3.15 (m, 1H), 2.74-2.79 (m, 1H), 2.37 (d, J=1.8Hz, 6H).

Step 2: Synthesis of(2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

(2R,3S,5R)-5-(5-bromo-4-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (4.50 g, 7.69 mmol) was added to NH₃ saturated i-PrOH(15 mL) at −60° C. The resulting mixture was stirred at 80° C. for 12hours, and then cooled down to room temperature and evaporated undervacuum to give(2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (4.2 g, 7.43 mmol) as a solid. This crude compound wasdissolved in 30 mL MeOH, and then sodium methanolate (14.86 mL, 14.86mmol) was added. After the resulting solution was stirred at roomtemperature for 2 hours, it was quenched with acetic acid (0.1 mL) andconcentrated under vacuum. The crude product was purified by silica gelcolumn chromatography by petroleum ether ethyl acetate (1:2) to give thetitle compound: ¹H-NMR (300 MHz, DMSO) δ 8.12 (s, 1H), 7.78 (s, 1H),6.78 (s, 2H), 6.48-6.51 (m, 1H), 5.25 (s, 1H), 5.01 (s, 1H), 4.32 (s,1H), 3.81 (s, 1H), 3.17 (s, 1H), 2.35-2.50 (m, 1H), 2.12-2.19 (m, 1H).

Step 3: Synthesis of5-bromo-7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine

Tert-butylchlorodimethylsilane (1.786 g, 11.85 mmol) was added to astirred solution of(2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(1.3 g, 3.95 mmol), 1H-imidazole (1.076 g, 15.80 mmol) in DMF (8 mL).The resulting mixture was stirred at room temperature for 4 hours, andthen diluted with 400 mL of ethyl acetate, washed with saturated aqueoussodium bicarbonate (80 mL) and saturated aqueous sodium chloride (80mL), dried over anhydrous sodium sulfate and concentrated in vacuum. Theresidue was purified by silica gel column chromatography with ethylacetate/petroleum ether (1:4) to give the title compound: ¹H-NMR (300MHz, DMSO) δ 8.10 (s, 1H), 7.55 (s, 1H), 6.79 (s, 2H), 6.48-6.53 (m,1H), 4.50 (s, 1H), 3.62-3.76 (m, 3H), 2.43-2.50 (m, 1H), 2.17-2.16 (m,1H), 0.88 (d, J=2.7 Hz, 18H), 0.10 (s, 6H), 0.05 (s, 6H).

Step 4: Synthesis of((2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)

5-bromo-7-((2R,4S,5R)-4-((tertbutyldimethylsilyl)oxy)-5-(((tertbutyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine(1.55 g, 2.78 mmol) was dissolved in THF (4 mL) and then treated with aprecooled solution of trifluoroacetic acid/water (v/v=1/1, 4 mL)dropwise with stirring at 0° C. in 10 minutes. After the resultingmixture was stirred at 0° C. for 2 hours, it was coevaporated withtoluene below 25° C. to give a pink syrup. The residue was applied ontoa silica gel column, eluted with ethyl acetate/dichloromethane (1/1) togive the title compound: ¹H-NMR (300 MHz, DMSO) δ 8.19 (s, 1H), 7.74 (s,1H), 7.28 (s, 2H), 6.50 (q, J=6.0 Hz, 2H), 4.51 (q, J=2.7 Hz, 1H), 3.81(s, 1H), 3.47-3.57 (m, 2H), 2.49-2.58 (m, 1H), 2.17-2.22 (m, 1H), 0.85(s, 9H), 0.09 (s, 6H).

Step 5: Synthesis of(2R,3S)-2-(((tert-butyldiphenylsilyl)oxy)methyl)-5-methoxy-2-phenyltetrahydrofuran-3-yl4-methylbenzoate

2-Iodoxybenzoic acid (839 mg, 3.00 mmol) was added to a solution of((2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol(443 mg, 0.999 mmol) in acetonitrile (45 mL). The resulting solution wasstirred at 80° C. for 2 hours, then cooled down to 0° C., filtered andconcentrated under reducing pressure. This resulted in the titlecompound, which was used to the next step directly without furtherpurification: MS(ES, m/z): 441.08[M+H]⁺.

Step 6: Synthesis of((2S,4R)-4-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-((tert-butyldimethylsilyl)oxy)cyclopentane-1,1-diyl)dimethanol

Sodium hydroxide (4.03 mL, 8.07 mmol) was added to a stirred solution of(2S,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde(445 mg, 1.008 mmol) and formaldehyde (1009 mg, 10.08 mmol) in dioxane(6 mL). The resulting mixture was stirred at room temperature for 3hours, and then diluted with 150 mL of ethyl acetate, washed withsaturated aqueous sodium bicarbonate (30 mL) and saturated aqueoussodium chloride (30 mL), dried over anhydrous sodium sulfate andconcentrated under vacuum to give a solid. Sodium borohydride (109 mg,2.88 mmol) was added to the solution of the prior solid in ethanol (15mL) at 0° C. The resulting solution was stirred at room temperature for2 hours, then quenched with acetic acid (0.1 mL) and concentrated underreducing pressure. The crude product was applied onto a silica gelcolumn chromatography by petroleum ether ethyl acetate (1:2) to give thetitle compound. MS(ES, m/z): 473.43 [M+H]⁺.

Step 7: Synthesis of(2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

2-Iodoxybenzoic acid (302 mg, 1.077 mmol) was added to a solution of((3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol(170 mg, 0.359 mmol) in acetonitrile (40 mL). After the resultingsolution was stirred at 0° C. for 12 hours, it was cooled down to 0° C.and then concentrated under reducing pressure to give the titlecompound, which was used to the next step directly without furtherpurification. MS(ES, m/z): 471.43[M+H]⁺.

Step 8: Synthesis of((2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol

Dimethyl (1-diazo-2-oxopropyl)phosphonate (139 mg, 0.721 mmol) was addedto a solution of(2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(170 mg, 0.361 mmol), potassium carbonate (125 mg, 0.902 mmol) inmethanol (8 mL) at 0° C. The resulting solution was stirred at roomtemperature for 12 hours, then filtered and concentrated under reducingpressure. The crude compound was purified by Prep-TLC by petroleumetherethyl acetate (1:2) to give the title compound. ¹H-NMR (300 MHz,CD₃OD, ppm) δ 8.00 (s, 1H), 7.39 (s, 1H), 6.44-6.47 (m, 1H), 4.62-4.66(m, 1H), 3.61-3.71 (m, 2H), 2.90 (s, 1H), 2.25-2.55 (m, 2H), 0.88 (s,9H), 0.57 (d, J=3 Hz, 6H).

Step 9: Synthesis of(2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol

((2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(40 mg, 0.086 mmol) and TBAF (0.086 mL, 0.086 mmol) was dissolved intoTHF (1 mL). The resulting solution was stirred for 2 hours at 30° C.,then evaporated and purified as following condition: Column: X BridgeC18, 19*150 mm, 5 um; Mobile Phase A:Water/0.05% TFA, Mobile Phase B:ACN; Flow rate: 20 mL/min; Gradient: 30% B to 70% B in 10 min; 254 nm.This resulted in compound 5 as a solid: ¹H-NMR (300 MHz, DMSO, ppm) δ8.11 (s, 1H), 7.59 (s, 1H), 6.52 (t, J=6.6 Hz, 1H), 4.48 (t, J=6.6 Hz,1H), 3.53-3.64 (m, 2H), 3.44 (s, 1H), 2.33-2.52 (m, 2H); MS (ES, m/z):353.17 [M+H]⁺.

Example 6: Synthesis of(2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(6)

Step 1: Synthesis of 4,5-dichloro-7H-pyrrolo[2,3-d]pyrimidine

To a mixture of 4-chloro-7H-pyrrolo[2,3-d]pyrimidine (2.5 g, 16.28 mmol)in dry DCM (100 mL) was added NCS (N-chlorosuccinimide) (4.35 g, 32.6mmol) at 25° C. The resulting mixture was stirred for 16 hours at 40° C.under argon atmosphere. When the 4-chloro-7H-pyrrolo[2,3-d]pyrimidinewas consumed, the mixture was filtered directly without cooling. Thesolid was collected, washed with DCM (20 mL), dried under vacuum to give4,5-dichloro-7H-pyrrolo[2,3-d]pyrimidine as a solid. LC-MS: (ES, m/z):188.01 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 12.90 (br, 1H), 8.65(s, 1H), 7.93 (d, J=2.7 Hz, 1H).

Step 2: Synthesis of(2R,3S,5R)-5-(4,5-dichloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

To a suspension of NaH (60% dispersion in mineral oil, 0.538 g, 13.46mmol) in anhydrous ACN (100 mL) under argon atmosphere in a 250 mL threenecked round-bottom flask, was added4,5-dichloro-7H-pyrrolo[2,3-d]pyrimidine (2.3 g, 12.23 mmol) in portionsand the mixture was stirred at ambient temperature for 30 minutes. Thecloudy mixture became clear and then(2R,3S)-5-chloro-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl-4-methylbenzoate(Intermediate A, 4.76 g, 12.23 mmol) was added portionwise with stirringin 5 minutes. The resulting mixture was heated to 50° C. and stirred for2 hours. The reaction progress was monitored by TLC. The volatile wasremoved under vacuum. The crude product was purified by silica gelcolumn chromatography using 10%-40% ethyl acetate in petroleum ether toafford the title compound. LC-MS: (ES, m/z): 540.39 [M+H]⁺. ¹H-NMR: (300MHz, CDCl₃, ppm): δ 8.64 (s, 1H), 7.91-7.99 (m, 4H), 7.39 (s, 1H),7.25-7.30 (m, 4H), 6.80 (t, J=6.9 Hz, 1H), 5.75 (dd, J=3.6 Hz, J=6.0 Hz,1H), 4.60-4.78 (m, 3H), 2.76-2.80 (m, 2H), 2.44 (d, J=4.8 Hz, 6H).

Step 3: Synthesis of(2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

To a 150 mL steel bomb, was placed(2R,3S,5R)-5-(4,5-dichloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (3.6 g, 6.66 mmol). The medium was cooled to −40° C. Tothis was added isopropanolic ammonia (isopropanol/liquid ammonia=1/3,v/v, 120 mL). The medium was sealed, heated to 90° C. and stirred for 16hours. TLC indicated that the started nucleoside was all consumed andtarget product was observed as a major product. The resulting mixturewas concentrated under vacuum. The crude product was purified by silicagel column chromatography using 2%-10% methanol in dichloromethane toafford the title compound. LC-MS: (ES, m/z): 284.70 [M+H]⁺. ¹H-NMR: (300MHz, d₆-DMSO, ppm): δ 8.09 (s, 1H), 7.58 (s, 1H), 6.87 (br, 2H), 6.51(dd, J=6.3 Hz, J=7.8 Hz, 1H), 5.25 (d, J=4.2 Hz, 1H), 5.03 (t, J=5.6 Hz,1H), 4.30-4.34 (m, 1H), 3.81 (dd, J=4.3 Hz, J=6.8 Hz, 1H), 3.46-3.60 (m,2H), 2.40-2.48 (m, 1H), 2.13-2.20 (m, 1H).

Step 4. Synthesis of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-4-amine

To a stirred solution of(2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(1.7 g, 5.97 mmol) in DMF (10 mL) was added 1H-imidazole (1.423 g, 20.90mmol) and TBDMS-Cl (2.70 g, 17.91 mmol) successively at 0° C. underargon atmosphere. The resulting mixture was warmed to 25° C. and stirredfor 2 hours. The resulting solution was diluted with ethyl acetate (100mL), washed with water (100 mL). The aqueous layer was re-extracted withethyl acetate (2×100 mL). The organic layers were combined, washed withsaturated aq NaHCO₃ (2×100 mL) and brine (2×100 mL) successively, driedover anhydrous Na₂SO₄, filtered and concentrated under vacuum. Theresidue was purified by silica gel column chromatography using 2%-10%ethyl acetate in petroleum ether to afford the title compound. LC-MS:(ES, m/z): 513.22 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ8.10 (s,1H), 7.50 (s, 1H), 6.85 (br, 2H), 6.51 (t, J=6.8 Hz, 1H), 4.48-4.52 (m,1H), 3.62-3.80 (m, 3H), 2.55-2.60 (m, 1H), 2.17-2.24 (m, 1H), 0.89 (s,18H), 0.08 (d, J=13.6 Hz, 12H).

Step 5. Synthesis of((2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol

To a stirred solution of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-4-amine(2.42 g, 4.72 mmol) in THF (48 mL) was added a pre-cooled solution oftrifluoroacetic acid/water (1/1, v/v, 24 mL) dropwise with stirring at0° C. in 10 minutes. The resulting mixture was stirred at 0° C. for 4hours. The reaction progress was monitored by TLC. The resultingsolution was co-evaporated with toluene (3×100 mL) while maintain theinner temperature below 25° C. The resulting crude material was purifiedby silica gel column chromatography using 2%-10% methanol indichloromethane to afford the title compound. LC-MS: (ES, m/z): 398.96[M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.28 (s, 1H), 7.86 (br, 2H),7.78 (s, 1H), 6.52 (t, J=6.8 Hz, 1H), 4.53 (t, J=2.6 Hz, 1H), 3.83 (dd,J=4.5 Hz, J=6.9 Hz, 1H), 3.48-3.60 (m, 2H), 2.50-2.58 (m, 1H), 2.18-2.25(m, 1H), 0.90 (s, 9H), 0.11 (s, 6H).

Step 6. Synthesis of(2S,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tertbutyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde

To a stirred solution of((2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol(300 mg, 0.752 mmol) in anhydrous ACN (30 mL) was added 2-Iodoxybenzoicacid (632 mg, 2.256 mmol) under argon atmosphere. The mixture was heatedto 85° C. and stirred for 20 minutes. The solid was filtered out. Thefiltrate was concentrated in vacuo to afford the title compound, whichwas used to the next reaction step directly without furtherpurification. LC-MS: (ES, m/z): 396.94 [M+H]⁺.

Step 7. Synthesis of((3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol

To a stirred solution of(2S,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde(434 mg, 0.820 mmol) in 1,4-dioxane (25 mL) in a 100 mL round-bottomflask, was added formaldehyde solution (5 mL), followed by the additionof sodium hydroxide solution (2 N, 5 mL, 10.00 mmol) dropwise at 0° C.in 5 minutes. The resulting mixture was warmed to 25° C. and stirred for3 hours. Upon the started nucleoside-aldehyde was all consumed, thereaction mixture was neutralized by the addition of AcOH. The mixturewas diluted with ethyl acetate (60 mL) and washed successively withwater (2×20 mL), saturated aqueous NaHCO₃ (2×20 mL) and brine (2×20 mL).The organic layer was dried over Na₂SO₄ and evaporated under reducedpressure. The residue was re-dissolved in anhydrous EtOH (30 mL) andadded sodium tetrahydroborate (62.0 mg, 1.640 mmol) in portions at 0° C.under argon atmosphere. After stirring for 16 hour at 25° C., thereaction mixture was neutralized by the addition of AcOH. The mixturewas concentrated under vacuum. The residue was suspended in CHCl₃ (40mL) and washed successively with water (2×15 mL) and brine (2×15 mL).The organic layer was dried over Na₂SO₄, filtered and concentrated undervacuum. The residue was purified by silica gel column chromatographywith dichloromethane/methanol (30/1) to give the title compound. LC-MS:(ES, m/z): 428.99 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.10 (s,1H), 7.60 (s, 1H), 6.86 (br, 2H), 6.54 (t, J=6.9 Hz, 1H), 5.01 (t, J=5.3Hz, 1H), 4.59 (dd, J=3.0 Hz, J=5.4 Hz, 1H), 4.40 (t, J=5.6 Hz, 1H),3.42-3.61 (m, 4H), 2.60-2.69 (m, 1H), 2.18-2.25 (m, 1H), 0.89 (s, 9H),0.09 (s, 6H).

Step 8. Synthesis of(2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

((3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol(166 mg, 0.387 mmol) was dissolved in anhydrous ACN (20 mL) under argonatmosphere and then IBX (325 mg, 1.161 mmol) was added. The resultingmixture was warmed to 30° C. and stirred for 20 hours. The solid wasfiltered out. The filtrate was concentrated in vacuo to afford the titlecompound, which was used to the next reaction step directly withoutfurther purification. LC-MS: (ES, m/z): 426.97 [M+H]⁺.

Step 9: Synthesis of((2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol

To a stirred solution of(2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(160 mg, 0.375 mmol) in dry MeOH (8 mL) was added K₂CO₃ (129 mg, 0.937mmol) followed by the addition of dimethyl(1-diazo-2-oxopropyl)phosphonate (144 mg, 0.749 mmol) at 0° C. dropwisewith stirring under argon atmosphere. The resulting mixture wasgradually warmed to 25° C. and stirred for 16 hours. The resultingmixture was concentrated under vacuum. The residue was purified bysilica gel column chromatography using 30%-50% ethyl acetate inpetroleum ether to afford the title compound. LC-MS: (ES, m/z): 422.98[M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.10 (s, 1H), 7.58 (s, 1H),6.90 (br, 2H), 6.52 (t, J=6.6 Hz, 1H), 5.42-5.46 (m, 1H), 4.64 (t, J=5.7Hz, 1H), 3.59-3.67 (m, 1H), 3.50-3.54 (m, 1H), 3.48 (s, 1H), 2.59-2.64(m, 1H), 2.27-2.31 (m, 1H), 0.91 (s, 9H), 0.12 (s, 6H).

Step 10: Synthesis of(2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(6)

To a stirred solution of((2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(64 mg, 0.151 mmol) in THF (3 mL) was added TBAF solution (1.0 M, 151μl, 0.151 mmol) dropwise with stirring under argon atmosphere. Theresulting solution was stirred for 1 hour at 25° C. The resultingmixture was concentrated under vacuum. The residue was applied onto asilica gel column and eluted with DCM/MeOH (20/1 to 5/1) to give crudeproduct. The crude product was further purified by Prep-HPLC with thefollowing conditions (1#-Pre-HPLC-011 (Waters)): Column, SunFire PrepC18 OBD (Optimum Bed Density) Column, 5 um, 19*150 mm; mobile phase,water (with 10 mmol ammonium bicarbonate) and acetonitrile (10%acetonitrile up to 45% in 5 min, up to 95% in 1.5 min, down to 5% in 1min); Detector, uv 254&220 nm. The product-containing fractions werecollected and lyophilized to give compound 6 as a solid. LC-MS: (ES,m/z): 308.72 [M+H]⁺. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.10 (s, 1H),7.54 (s, 1H), 6.88 (br, 2H), 6.52 (t, J=6.4 Hz, 1H), 5.39-5.52 (m, 2H),4.48 (t, J=6.6 Hz, 1H), 3.59 (dd, J=12.0 Hz, J=28.8 Hz, 2H), 3.48 (s,1H), 2.47-2.54 (m, 1H), 2.31-2.37 (m, 1H).

Intermediate B Synthesis of((2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(Intermediate B)

Step 1: Synthesis of 4-chloro-5-iodo-7H-pyrrolo[2,3-d]pyrimidine

To a mixture of 4-chloro-7H-pyrrolo[2,3-d]pyrimidine (5 g, 32.6 mmol) inDMF (60 mL) under argon was added NIS (N-iodosuccinimide) (7.33 g, 32.6mmol) at 0° C. The resulting mixture was stirred for 15 hours at 25° C.under a atmosphere of argon in the darkness. The reaction mixture waspoured into cold water and the mixture was filtered, the solid waswashing with cold water (3×50 mL) and dried at 25° C. to give4-chloro-5-iodo-7H-pyrrolo[2,3-d]pyrimidine as a solid. LC-MS: (ES,m/z): 279.9 [M+H]⁺¹. ¹H-NMR: (400 MHz, CD₃SOCD₃, ppm): 12.96 (brs, 1H),8.62 (s, 1H), 7.95 (d, J=1.8 Hz, 1H)

Step 2: Synthesis of(2R,3S,5R)-5-(4-chloro-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

To a mixture of sodium hydride (0.845 g, 21.13 mmol) and4-chloro-5-iodo-7H-pyrrolo[2,3-d]pyrimidine (5.37 g, 19.21 mmol) inacetonitrile (150 mL) under argon was added(2R,3S,5R)-5-chloro-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (7.47 g, 19.21 mmol) at 20° C. The resulting mixturewas stirred for 2 hours at 50° C. under a atmosphere of argon and thenthe solvent was evaporated under reduce pressure. The residue waspurified by column chromatography on silica gel 100-200, eluting withEA/PE (1/5) to give the title compound. LC-MS: (ES, m/z): δ13.9 [M+H]⁺¹.¹H-NMR: (400 MHz, CDCl₃, ppm): 8.63 (s, 1H), 8.00 (d, J=8.4 Hz, 2H),7.95 (d, J=8.4 Hz, 2H), 7.60 (s, 1H), 7.32-7.25 (m, 4H), 6.82 (t, J=7.2Hz, 1H), 5.77 (dd, J=6.4 Hz, 4 Hz, 1H), 4.80-4.76 (m, 1H), 4.71-4.62 (m,2H), 2.46 (s, 6H), 1.66-1.31 (m, 2H)

Step 3: Synthesis of(2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

(2R,3S,5R)-5-(4-chloro-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (12 g, 18.99 mmol) was added to a stirred, cooled −50°C. mixture of ammonia (120 mL, 240 mmol) in 2-Propanol (30 mL) and themixture was stirred at 90° C. for 48 hours. The solvent was evaporatedunder reduce pressure. The residue was purified by column chromatographyon silica gel 100-200, eluting with DCM/MeOH (10/1) to give the titlecompound. LC-MS: (ES, m/z): 377.0 [M+H]⁺. ¹H-NMR: (300 MHz, CD₃SOCD₃,ppm): 8.10 (s, 1H), 7.81 (s, 1H), 6.79 (brs, 2H), 6.79-6.51 (dd, J=8.1Hz, 3 Hz, 1H), 5.27 (d, J=3.9 Hz, 1H), 5.05 (t, J=5.4 Hz, 1H), 4.33(brs, 1H), 3.81 (brs, 1H), 3.60-3.46 (m, 2H), 2.51-2.44 (m, 1H),2.19-2.10 (m, 1H)

Step 4: Synthesis of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-4-amine

To a mixture of(2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(6 g, 15.95 mmol) and imidazole (4.34 g, 63.8 mmol) in DMF (30 mL) underargon was added TBS-Cl (44.7 mL, 44.7 mmol) at 0° C. The resultingmixture was stirred for 2 hours at 23° C. under a atmosphere of argon.The reaction progress was monitored by LCMS. The reaction mixture wasquenched with water (150 mL) and extracted with ethyl acetate (3×200mL). The combined organic layers was washed with brine (5×200 mL), driedover anhydrous sodium sulfate and filtered. The filtrate wasconcentrated under reduced pressure, the residue was purified by asilica gel column, eluting with EA/PE (3:7) to afford the titlecompound. LC-MS: (ES, m/z): δ05.3 [M+H]⁺¹. ¹H-NMR: (400 MHz, CD₃SOCD₃,ppm): 8.10 (s, 1H), 7.58 (s, 1H), 6.67 (brs, 2H), 6.49 (t, J=6.8 Hz,1H), 4.50 (t, J=2.4 Hz, 1H), 3.88-3.81 (m, 1H), 3.74 (dd, J=10.8 Hz, 5.6Hz, 1H), 3.65 (dd, J=10.8 Hz, 4 Hz, 1H), 2.50-2.49 (m, 1H), 2.25-2.14(m, 1H), 0.89 (s, 18H), 0.10-0.07 (m, 12H).

Step 5: Synthesis of((2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol

To a mixture of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-4-amine(6.6 g, 10.92 mmol) in THF (66 mL) was added a solution of TFA (16 mL,208 mmol) in Water (16 mL) at 0° C. The resulting mixture was stirredfor 4 hour at 0° C. The reaction progress was monitored by LCMS. Thesolvent was evaporated under reduced pressure. The residue was dissolvedin DCM/MeOH (10/1, 150 mL) and the pH value of the solution was adjustedto 7 with sodium hydrogen carbonate (5.0 g), filtered and the solventwas evaporated under reduced pressure. The residue was purified bycolumn chromatography on silica gel 100-200, eluting with 40-50% EA inPE to give the title compound. LC-MS: (ES, m/z): 491.1 [M+H]⁺¹. ¹H-NMR:(400 MHz, CD₃SOCD₃, ppm): 8.14 (s, 1H), 7.71 (s, 1H), 6.88 (brs, 2H),6.47 (dd, J=8.4 Hz, 6 Hz, 1H), 4.51 (t, J=2.4 Hz, 1H), 3.80-3.79 (m,1H), 3.54-3.50 (m, 2H), 2.57-2.53 (m, 1H), 2.18-2.13 (m, 1H), 0.89 (s,9H), 0.10 (s, 6H).

Step 6: Synthesis of(2S,3S,5R)-3-[(tert-butyldimethylsilyl)oxy]-5-{4-[(dimethyl-Si{4}-sulfanylidene)amino]-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl}oxolane-2-carbaldehyde

To a mixture of((2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol(4.682 g, 9.55 mmol) and DCC (N,N-dicyclohexylcarbodiimide) (6.1 g, 29.6mmol) in DMSO (40 mL) under argon were added pyridine (0.850 mL, 10.51mmol) and TFA (0.515 mL, 6.68 mmol) at 0° C. The resulting mixture wasstirred for 14 hours at 20° C. under argon. The reaction progress wasmonitored by LCMS. The reaction mixture was quenched with water (150 mL)and extracted with ethyl acetate (3×100 mL). The combined organic layerswas washed with brine (120 mL), dried over anhydrous sodium sulfate andfiltered. The filtrate was concentrated under reduced pressure to affordcrude title product as a solid. LC-MS: (ES, m/z): 567.0 [M+H₂O+H]⁺

Step 7: Synthesis of mixture of[(3S,5R)-3-[(tert-butyldimethylsilyl)oxy]-5-{4-[(dimethyl-Si{4}-sulfanylidene)amino]-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl}-2-(hydroxymethyl)oxolan-2-yl]methanol

To a mixture of(2S,3S,5R)-3-[(tert-butyldimethylsilyl)oxy]-5-{4-[(dimethyl-Si{4}-sulfanylidene)amino]-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl}oxolane-2-carbaldehyde(80 mg, 0.146 mmol) and formaldehyde (0.5 mL, 0.146 mmol) in 1,4-Dioxane(4 mL) was added 2 M sodium hydroxide (0.5 mL, 1.000 mmol) at 0° C. Theresulting mixture was stirred for 4 hours at 20° C. The reactionprogress was monitored by LCMS. The reaction mixture was quenched withacetic acid (0.2 mL) and extracted with ethyl acetate (3×40 mL). Thecombined organic layers was washed with sat. NaHCO₃ (30 mL) then brine(40 mL), dried over anhydrous sodium sulfate and filtered. The filtratewas concentrated under reduced pressure, the residue was dissolved inEthanol (4 mL). This mixture was added sodium tetrahydroborate (20 mg,0.529 mmol) under argon. This mixture was stirred for 36 hours at 20° C.The reaction progress was monitored by LCMS. The reaction mixture wasquenched with acetic acid (0.05 mL) and extracted with CHCl₃ (3×40 mL).The combined organic layers was washed with sat. NaHCO₃ (30 mL) thenbrine (40 mL), dried over anhydrous sodium sulfate and filtered. Thefiltrate was concentrated under reduced pressure, purified by TLC,eluting with DCM/MeOH (12:1) to afford the title compound. LC-MS: (ES,m/z): 581.1 [M+H]⁺¹. ¹H-NMR: (300 MHz, CD₃SOCD₃, ppm): 8.09 (s, 0.6H),7.97 (s, 0.4H), 7.69 (s, 0.6H), 7.46 (s, 0.4H), 6.66 (brs, 0.8H),6.53-6.42 (m, 1H), 5.10 (t, J=5.4 Hz, 0.4H), 5.02 (t, J=5.4 Hz, 0.6H),4.58 (brs, 1H), 4.42-4.37 (m, 1H), 3.58-3.49 (m, 4H), 2.78 (d, J=2.7 Hz,3H), 2.68-2.61 (m, 1H), 2.23-2.16 (m, 1H), 0.90 (s, 9H), 0.10 (s, 6H).

Step 8: Synthesis of((3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol

To a solution of[(3S,5R)-3-[(tert-butyldimethylsilyl)oxy]-5-{4-[(dimethyl-Si{4}-sulfanylidene)amino]-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl}-2-(hydroxymethyl)oxolan-2-yl]methanol(230 mg, 0.396 mmol) in DCM (2 mL) was added TFA (2 mL, 26.0 mmol) at 0°C. The resulting mixture was stirred for 3 hours at 20° C. under argon.The reaction progress was monitored by LCMS. The reaction mixture wasconcentrated under reduced pressure, the residue was purified by asilica gel column, eluting with DCM/MeOH (95:5) to afford the titlecompound. LC-MS: (ES, m/z): 521.2 [M+H]⁺. ¹H-NMR: (400 MHz, CD₃SOCD₃,ppm): 8.12 (s, 1H), 7.71 (s, 1H), 7.10 (brs, 2H), 6.43 (t, J=6.8 Hz,1H), 4.50 (dd, J=6 Hz, 3.2 Hz, 1H), 3.50-3.37 (m, 4H), 2.59-2.52 (m,1H), 2.17-2.11 (m, 1H), 0.80 (s, 9H), 0.00 (s, 6H).

Step 9: Synthesis of(2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

To a solution of((3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol(960 mg, 1.845 mmol) in Acetonitrile (25 mL) under argon was added IBX(1550 mg, 5.53 mmol) at 18° C. The resulting mixture was stirred for 18hours at 18° C. under argon. The reaction progress was monitored byLCMS. The reaction mixture was filtered. The filtrate was concentratedunder reduced pressure, to afford the crude product as a solid. Thiscrude product was used for next step directly without furtherpurification. LC-MS: (ES, m/z): 519.1 [M+H]⁺

Step 10: Synthesis of((2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(Intermediate B)

To a mixture of(2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(190 mg, 0.366 mmol) and K₂CO₃ (127 mg, 0.916 mmol) in MeOH (10 mL)under argon was added dimethyl (1-diazo-2-oxopropyl)phosphonate (141 mg,0.733 mmol) at 0° C. The resulting mixture was stirred for 16 hours at18° C. under argon. The color of the mixture turned from yellow to blue.The reaction progress was monitored by LCMS/TLC. The reaction mixturewas concentrated under reduced pressure, the residue was purified by asilica gel column, eluting with DCM/MeOH (97:3) to afford the titlecompound. LC-MS: (ES, m/z): 515.1 [M+H]⁺¹. ¹H-NMR: (400 MHz, CDCl₃,ppm): 8.22 (s, 1H), 7.12 (s, 1H), 6.25 (dd, J=8.8 Hz, 5.6 Hz, 1H), 5.84(brs, 2H), 4.71 (dd, J=5.6 Hz, 2 Hz, 1H), 4.01 (d, J=12.4 Hz, 1H), 3.80(d, J=16 Hz, 1H), 3.17-3.10 (m, 1H), 2.59 (s, 1H), 2.27-2.21 (m, 1H),0.91 (s, 9H), 0.11 (s, 6H)

Example 7: Synthesis of(2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(7)

To a solution of((2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(Intermediate B, 20 mg, 0.039 mmol) in tetrahydrofuran (3 mL) underargon was added TBAF (0.05 mL, 0.050 mmol) at 18° C. The resultingmixture was stirred for 0.5 hours at 18° C. under argon. The reactionprogress was monitored by TLC. The reaction mixture was concentratedunder reduced pressure, the residue was purified by a silica gel column,eluting with CH₂Cl₂/MeOH (7:1), to give crude product which was purifiedby Prep-HPLC with the following conditions: Instrument, Water-1 (26);Column: Xbridge RP 18, 5 um, 19×150 mm; mobile phase: water (0.05%Ammonium bicarbonate+Carbon dioxide) and acetonitrile (10% acetonitrileup to 40% in 8 min, hold 100% for 2 min, down to 10% in 2 min);Detector, UV 220 and 254 nm. The collected fractions were combined andconcentrated under reducing pressure to give compound 7 as a solid.LC-MS: (ES, m/z): 401.0[M+H]⁺. ¹H-NMR: (400 MHz, CD₃OD): δ8.10 (s, 1H),7.63 (s, 1H), 6.68 (s, 2H), 6.49 (t, J=6.4 Hz, 1H), 5.52 (d, J=5.2 Hz,1H), 4.48 (q, J=6.0 Hz, 1H), 3.64-3.60 (m, 1H), 3.57-3.52 (m, 1H), 3.48(s, 1H), 2.53-2.47 (m, 1H), 2.35-2.29 (m, 1H).

Example 8: Synthesis of(2R,3S,5R)-5-(2,4-diamino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(8)

Step 1: Synthesis of(2R,3S,5R)-5-(2-amino-4-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

To a mixture of 4-chloro-7H-pyrrolo[2,3-d]pyrimidin-2-amine (2.0 g,11.86 mmol) and NaH (0.524 g, 13.09 mmol) in acetonitrile (60 mL) underargon was stirred for 0.5 hours at room temperature under a argon. Themixture was then added Intermediate A (4.628 g, 11.90 mmol), stirred for10 minutes at room temperature then 50° C. for 2 hours. The process wasmonitored by LCMS. The reaction mixture was concentrated under reducedpressure, the residue was purified by a silica gel column, eluting withCH₂Cl₂/MeOH (92:8) to afford the title compound. LC-MS: (ES, m/z):521.1[M+H]⁺. ¹H-NMR: (300 MHz, DMSO-d₆): δ 7.93 (dd, J=8.1 Hz, 4H),7.68-7.21 (m, 5H), 6.78 (s, 2H), 6.57 (q, J=5.85 Hz, 1H), 6.39 (d, J=3.9Hz, 1H), 5.69 (d, J=5.7 Hz, 1H), 4.63-4.43 (m, 3H), 3.04-2.94 (m, 1H),2.66 (dd, J=4.95 Hz, 1H), 2.41 (d, J=7.8 Hz, 6H), 1.99 (s, 1H).

Step 2: Synthesis of(2R,3S,5R)-5-(2,4-diamino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

To a mixture of(2R,3S,5R)-5-(2-amino-4-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (1.0 g, 0.960 mmol) and ammonia (50 mL, 0.960 mmol) in2-Propanol (5 mL) was stirred for 20 hours at 100° C. The reactionprogress was monitored by TLC. The reaction mixture was allowed to coolto ambient temperature, and concentrated under reduced pressure, theresidue was purified by a silica gel column, eluting with CH₂Cl₂/MeOH(82:18) to afford the title compound. LC-MS: (ES, m/z): 266.0[M+H]⁺.¹H-NMR: (300 MHz, DMSO-d₆): δ 6.93 (d, J=3.6 Hz, 1H), 6.76 (s, 2H), 6.40(d, J=3.6 Hz, 1H), 6.32 (q, J=5.85 Hz, 1H), 5.70 (s, 2H), 5.20 (d, J=3.6Hz, 1H), 4.29 (d, J=2.4 Hz, 1H), 3.78-3.74 (m, 1H), 3.55-3.41 (m, 2H),3.16 (s, 1H), 2.49-2.34 (m, 1H), 2.08-2.01 (m, 1H).

Step 3: Synthesis of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamine

To a mixture of(2R,3S,5R)-5-(2,4-diamino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(1.39 g, 5.24 mmol) and TBDMS-Cl (2.369 g, 15.72 mmol) in DMF (6 mL)under argon was added imidazole (1.784 g, 26.2 mmol). The resultingmixture was stirred for 16 hours at 20° C. under a argon atmosphere. Thereaction progress was monitored by LCMS/TLC. The reaction mixture wasconcentrated under reduced pressure, the residue was purified by asilica gel column, eluting with CH₂Cl₂/MeOH (92:8) to afford the titlecompound as a solid. LC-MS: (ES, m/z): 494.4 [M+H]⁺, ¹H-NMR: (300 MHz,CDCl₃): δ 7.58 (s, 2H), 7.04 (d, J=3.9 Hz, 1H), 6.54 (d, J=3.9 Hz, 1H),6.52 (s, 2H), 6.32 (dd, J=6.0 Hz, 1H), 4.45 (t, J=2.4 Hz, 1H), 3.78 (d,J=2.1 Hz, 1H), 3.68 (t, J=5.5 Hz, 2H), 3.17 (d, J=3.0 Hz, 1H), 2.49-2.42(m, 1H), 2.17-2.10 (m, 1H), 0.89 (s, 18H), 0.10-0.09 (m, 12H).

Step 4: Synthesis ofN,N′-(7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide

To a mixture of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamine(138 mg, 0.279 mmol) and DMAP (5 mg, 0.041 mmol) in pyridine (5 mL)under argon was added benzoyl chloride (158 mg, 1.124 mmol). Theresulting mixture was stirred for 4 hours at 0° C. under argon. Thereaction progress was monitored by LCMS/TLC. The reaction mixture wasquenched by water (50 mL) and extracted with ethyl acetate (3×30 mL).The combined organic layers was washed with brine (40 mL), dried overanhydrous sodium sulfate and filtered. The filtrate was concentratedunder reduced pressure, the residue was purified by a silica gel column,eluting with PE/EA (2:1) to provide the title compound. LC-MS: (ES,m/z): 702.3[M+H]⁺, ¹H-NMR: (300 MHz, CDCl₃): δ 11.11 (s, 1H), 10.80 (s,1H), 8.09 (d, J=7.2 Hz, 2H), 7.73 (d, J=7.2 Hz, 2H), 7.66-7.43 (m, 8H),6.62-6.54 (m, 2H), 4.56 (s, 1H), 3.84-3.64 (m, 4H), 2.81-2.72 (m, 1H),2.26-2.22 (m, 1H), 0.90-0.83 (m, 18H), 0.11-0.01 (m, 12H).

Step 5: Synthesis ofN,N′-(7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(hydroxymethyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide

To a mixture ofN,N′-(7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide(110 mg, 0.157 mmol) in THF (4 mL) was added a solution of TFA (0.5 mL,6.49 mmol) in Water (0.5 mL) at 0° C. The resulting mixture was stirredfor 4 hours at 0° C. The reaction progress was monitored by LCMS. Thereaction mixture was concentrated under reduced pressure, the residuewas purified by a silica gel column, eluting with CH₂Cl₂/MeOH (95:5) toafford the title compound. LC-MS: (ES, m/z): 588.6[M+H]⁺, ¹H-NMR: (300MHz, CDCl₃): δ 11.11 (s, 1H), 10.81 (s, 1H), 8.09 (d, J=7.2 Hz, 2H),7.97 (d, J=7.2 Hz, 2H), 7.65-7.46 (m, 8H), 6.62-6.56 (m, 2H), 4.96 (t,J=5.4 Hz, 1H), 4.58 (t, J=2.7 Hz, 1H), 3.82-3.77 (m, 2H), 3.56-3.51 (m,2H), 2.72-2.67 (m, 1H), 2.27-2.21 (m, 1H), 0.88 (s, 9H), 0.09 (s, 6H).

Step 6: Synthesis ofN,N′-(7-((2R,4S,5S)-4-((tert-butyldimethylsilyl)oxy)-5-formyltetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide

To a mixture ofN,N′-(7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(hydroxymethyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide(35 mg, 0.060 mmol) in acetonitrile (5 mL) under argon was added IBX (42mg, 0.150 mmol). The resulting mixture was stirred for 50 minutes at 50°C. under a argon. The reaction progress was monitored by LCMS. Thereaction mixture was allowed to cool to ambient temperature andfiltered. The filtrate was concentrated under reduced pressure, thecrude product was used for next step directly without furtherpurification. LC-MS: (ES, m/z): δ18.3 [M+CH₃OH]⁺

Step 7: Synthesis ofN,N′-(7-((2R,4S)-4-((tert-butyldimethylsilyl)oxy)-5,5-bis(hydroxymethyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide

To a solution ofN,N′-(7-((2R,4S,5S)-4-((tert-butyldimethylsilyl)oxy)-5-formyltetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide(35 mg, 0.060 mmol) in 1,4-Dioxane (5 mL), was added formaldehyde (1 mL,0.060 mmol), NaOH (1 mL, 2.000 mmol), the mixture was stirred for 4hours at 20° C., cooled to 0° C., quenched with AcOH to pH 6, addedwater (40 mL) and extracted with ethyl acetate (3×40 mL). The combinedorganic layers was washed with brine (30 mL), dried over anhydroussodium sulfate and filtered. The filtrate was concentrated under reducedpressure, the residue was dissolved in ethanol (5.00 mL), added NaBH₄(5.65 mg, 0.149 mmol) under argon. The resulting mixture was stirred for16 hours at 20° C. The reaction progress was monitored by LCMS. Thereaction mixture was allowed to cool to ambient temperature, quenchedwith AcOH to PH 6, added water (40 mL) and extracted with ethyl acetate(3×40 mL). The organic layers were concentrated and purified by a silicagel column, eluting with CH₂Cl₂/MeOH (20:1) to afford the title productas a solid. LC-MS: (ES, m/z): 618.2 [M+H]f, ¹H-NMR: (400 MHz, CDCl₃): δ11.11 (s, 1H), 10.80 (s, 1H), 8.09 (d, J=7.2 Hz, 2H), 7.73 (d, J=7.2 Hz,2H), 7.66-7.43 (m, 8H), 6.62-6.54 (m, 2H), 4.56 (s, 1H), 3.84-3.64 (m,4H), 2.81-2.72 (m, 1H), 2.26-2.22 (m, 1H), 0.90-0.83 (m, 18H), 0.11-0.01(m, 12H).

Step 8: Synthesis ofN,N′-(7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-formyl-5-(hydroxymethyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide

To a solution ofN,N′-(7-((2R,4S)-4-((tert-butyldimethylsilyl)oxy)-5,5-bis(hydroxymethyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide(30 mg, 0.049 mmol) in acetonitrile (10 mL) under argon was added IBX(40 mg, 0.143 mmol) at 20° C. The resulting mixture was stirred for 3hours at 25° C. under argon. The reaction progress was monitored byLCMS. The reaction mixture was allowed to cool to ambient temperatureand filtered. The filtrate was concentrated under reduced pressure toafford crude product as a solid used for next step directly withoutfurther purification. LC-MS: (ES, m/z): δ16.2 [M+H]⁺

Step 9: Synthesis ofN,N′-(7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-ethynyl-5-(hydroxymethyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide

To a mixture ofN,N′-(7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-formyl-5-(hydroxymethyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide(70 mg, 0.114 mmol) and K₂CO₃ (39.3 mg, 0.284 mmol) in MeOH (5 mL) underargon was added a solution of dimethyl(2-diazo-3-oxobutanoyl)phosphonate (50.0 mg, 0.227 mmol) in MeOH (0.25mL) at 0° C. The resulting mixture was stirred for 16 hours at 25° C.under argon. The reaction progress was monitored by LCMS. The reactionmixture was concentrated under reduced pressure, the residue waspurified by TLC, eluting with CH₂Cl₂/MeOH (20:1) to afford the titlecompound. LC-MS: (ES, m/z): δ12.4[M+H]⁺

Step 10: Synthesis of(2R,3S,5R)-5-(2,4-diamino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(8)

To a solution ofN,N′-(7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-ethynyl-5-(hydroxymethyl)tetrahydrofuran-2-yl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diyl)dibenzamide(40 mg, 0.065 mmol) in MeOH (4 mL) under argon was added a solution ofNaOCH₃ in MeOH (0.065 mL, 0.065M) at 20° C. The resulting mixture wasstirred for 48 hours at 40° C. under argon. The reaction progress wasmonitored by LCMS. The reaction mixture was allowed to cool to ambienttemperature, and concentrated under reduced pressure, the residue waspurified by TLC, eluting with CH₂C₂/MeOH (20:1) to afford crudeintermediate (27 mg) as a solid which was diluted in THF (3 mL) underargon. Added a solution of TBAF (1M, 0.040 mL, 0.04 mmol) at 20° C. Theresulting mixture was stirred for 0.5 hours at 20° C. under argon. Thereaction progress was monitored by LCMS/TLC. The reaction mixture wasconcentrated under reduced pressure, the residue was purified by TLC,eluting with CH₂Cl₂/MeOH (5:1) to afford crude product (15 mg) then waspurified by Prep-HPLC with the following conditions: Instrument,Waters-2767-Prep; Column: Xbridge RP18, 5 um, 19×150 mm; mobile phase:water (0.05% Ammonium bicarbonate (carbon dioxide) and acetonitrile (5%acetonitrile up to 40% in 8 min); Detector, UV 220 and 254 nm. Thecollected fractions were combined and concentrated under reducingpressure to give compound 8 as a solid. LC-MS: (ES, m/z): δ18.2 [M+H]⁺,¹H-NMR: (400 MHz, CDCl₃): δ 6.85 (d, J=3.6 Hz, 1H), 6.55 (s, 2H), 6.36(d, J=4.0 Hz, 2H), 5.56 (s, 2H), 5.48-5.43 (m, 2H), 4.42 (q, J=5.6 Hz,1H), 3.61-3.49 (m, 2H), 3.44 (s, 1H), 2.47-2.40 (m, 1H), 2.26-2.21 (m,1H).

Example 9: Synthesis of(2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(9)

Step 1: Synthesis of 4-azido-7H-pyrrolo[2,3-d]pyrimidin-2-amine

To a stirred solution of 4-chloro-7H-pyrrolo[2,3-d]pyrimidin-2-amine(3.5 g, 20.76 mmol) in anhydrous DMSO (35 mL) under argon atmosphere,was added a solution of sodium azide (2.025 g, 31.1 mmol) in water (3.50mL). The mixture was heated to 100° C. and stirred overnight. Thereaction progress was monitored by TLC & LCMS. The resulting mixture wascooled to ambient temperature. 250 g crushed ice was added and themixture was stirred at 0° C. for 30 minutes. A precipitate was formed.The precipitate was collected by filtration, washed with cold water anddried over P₂O₅ under vacuum overnight to give4-azido-7H-pyrrolo[2,3-d]pyrimidin-2-amine as a solid, which was used tothe next reaction step directly without further purification. ¹H-NMR:(400 MHz, d₆-DMSO, ppm): δ 11.91 (brs, 1H), 7.96 (brs, 2H), 7.13 (t,J=3.0 Hz, 1H), 6.72 (dd, J=2.0 Hz, J=3.2 Hz, 1H). LC-MS: (ES, m/z):176.00 [M+H]⁺.

Step 2: Synthesis of 4-azido-2-fluoro-7H-pyrrolo[2,3-d]pyrimidine

Hydrogen fluoride-pyridine (70% HF in 30% Py) (12 mL, 133 mmol) wasmassed into a teflon bottle under argon atmosphere. To this was added4-azido-7H-pyrrolo[2,3-d]pyrimidin-2-amine (3.1 g, 17.70 mmol). Themixture was stirred at ambient temperature until it became a clearsolution, then cooled to −60° C., followed by the addition of tert-butylnitrite (2.5 mL, 21.02 mmol) drop-wised in 10 minutes. The resultingmixture was stirred between −60° C. to −40° C. for 2 hours. The reactionprogress was monitored by TLC & LCMS. The mixture was poured into coldaqueous NaHCO₃ (150 mL, saturated). The crude product was extracted withethyl acetate (100 mL×3), washed with brine (100 mL×2), dried overanhydrous Na₂SO₄, filtered and the filtrate was concentrated undervacuum to give a residue. The residue was then purified by silica gelcolumn chromatography using ethyl acetate/petroleum ether (1/4) to give4-azido-2-fluoro-7H-pyrrolo[2,3-d] as a solid. ¹H-NMR: (300 MHz,d₆-DMSO, ppm): δ 12.43 (brs, 1H), 7.48 (d, J=3.9 Hz, 1H), 6.50 (d, J=3.6Hz, 1H). F-NMR: (282 MHz, d₆-DMSO, ppm): δ−54.57 (s, 1F). LC-MS: (ES,m/z): 179.20 [M+H]⁺.

Step 3: Synthesis of(2R,3S,5R)-5-(4-azido-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

To a stirred suspension of sodium hydride 60% dispersion in mineral oil(0.272 g, 6.79 mmol) in anhydrous DMF (20 mL) under argon atmosphere ina 50 mL two necked round-bottom flask, was added4-azido-2-fluoro-7H-pyrrolo[2,3-d]pyrimidine (1.1 g, 6.18 mmol) inportions at 0° C. and the mixture was stirred at this temperature for 5minutes. Intermediate A (2.4 g, 6.17 mmol) was added with stirring. Thereaction mixture was warmed to 25° C. and stirred for 2 hours. Thereaction progress was monitored by TLC & LCMS. The mixture was dilutedwith ethyl acetate (100 mL), washed with water (70 mL). The aqueouslayer was re-extracted with ethyl acetate (60 mL×2). The combinedorganic layer was washed with brine (100 mL×3), dried over anhydrousNa₂SO₄, filtered and concentrated under vacuum. The crude product waspurified by silica gel column chromatography using ethylacetate/petroleum ether (1/10) to give the title compound. ¹H-NMR: (400MHz, CDCl₃, ppm): δ 8.00 (d, J=8.4 Hz, 2H), 7.95 (d, J=8.0 Hz, 2H),7.32-7.23 (m, 4H), 6.74 (dd, J=6.4 Hz, J=8.0 Hz, 1H), 6.49 (d, J=4.0 Hz,1H), 5.75-5.74 (m, 1H), 4.75-4.54 (m, 3H), 2.85-2.74 (m, 2H), 2.47-2.43(m, 6H). F-NMR: (376 MHz, CDCl₃, ppm): δ−52.26 (s, 1F, β isomer), −52.48(s, 1F, α isomer). LC-MS: (ES, m/z): 531.42 [M+H]⁺.

Step 4: Synthesis of(2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate

To a stirred solution of(2R,3S,5R)-5-(4-azido-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (2.0 g, 3.77 mmol) in a mixture of MeOH (10 mL) and DCM(15 mL) under argon atmosphere, was added propane-1,3-dithiol (0.816 g,7.54 mmol), followed by the addition of triethylamine (0.763 g, 7.54mmol) dropwise with stirring in 10 minutes at 25° C. The mixture wasstirred at 25° C. for 30 minutes. The reaction progress was monitored byTLC. The resulting mixture was concentrated under vacuum. The residuewas then purified by silica gel column chromatography using ethylacetate/petroleum ether (42% EA in PE) to give the title compound as apowder. ¹H-NMR: (400 MHz, CDCl₃, ppm): δ 8.00 (d, J=8.0 Hz, 2H), 7.97(d, J=8.0 Hz, 2H), 7.33-7.26 (m, 4H), 7.12 (d, J=4.0 Hz, 1H), 6.72 (dd,J=6.2 Hz, J=8.2 Hz, 1H), 6.38 (d, J=3.6 Hz, 1H), 5.75-5.72 (m, 1H), 5.36(brs, 2H), 4.73-4.57 (m, 3H), 2.79-2.74 (m, 2H), 2.47 (s, 3H), 2.44 (s,3H). F-NMR: (376 MHz, CDCl₃, ppm): δ−52.97 (s, 1F, β isomer), −53.10 (s,1F, α isomer). LC-MS: (ES, m/z): 505.63 [M+H]⁺.

Step 5: Synthesis of(2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

To a stirred solution of(2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(((4-methylbenzoyl)oxy)methyl)tetrahydrofuran-3-yl4-methylbenzoate (1.75 g, 3.47 mmol) in anhydrous MeOH (10 mL) underargon atmosphere, was injected sodium methoxide MeOH solution (1.0 M,3.47 mL, 3.47 mmol) with stirring at 0° C. in 5 minutes. The resultingmixture was allowed to stir at 0° C. to 10° C. for 4 hours. The reactionprogress was monitored by TLC & LCMS. The resulting mixture wasneutralized by the addition of AcOH, then concentrated under reducedpressure. The residue was then purified by silica gel columnchromatography using dichloromethane/methanol (6% MeOH in DCM) to givethe title compound. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 7.55 (brs, 2H),7.31 (d, J=3.6 Hz, 1H), 6.61 (d, J=3.6 Hz, 1H), 6.34 (dd, J=6.4 Hz,J=8.0 Hz, 1H), 5.26 (d, J=3.6 Hz, 1H), 4.92 (t, J=5.0 Hz, 1H), 4.32 (d,J=2.4 Hz, 1H), 3.82-3.79 (m, 1H), 3.58-3.46 (m, 2H), 2.48-2.41 (m, 1H),2.19-2.13 (m, 1H). F-NMR: (376 MHz, d₆-DMSO, ppm): δ−53.77 (s, 1F, βisomer), −53.98 (s, 1F, α isomer). LC-MS: (ES, m/z): 269.20 [M+H]⁺.

Step 6: Synthesis of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-4-amine

(2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(850 mg, 3.17 mmol) and imidazole (863 mg, 12.68 mmol) were massed intoa 50 mL round bottom flask under argon atmosphere. To the flask wasinjected anhydrous DMF (10 mL), followed by the addition of TBS-Cl (1433mg, 9.51 mmol) in portions. The mixture was stirred at 25° C. for 2hours. After The reaction reached to complete, the mixture was dilutedwith ethyl acetate (60 mL), washed with water (30 mL×2), aqueous NaHCO₃(saturated, 30 mL×2) and brine (30 mL×2) respectively. The organic layerwas collected and dried over anhydrous Na₂SO₄, filtered and concentratedunder reduced pressure to give crude product. The residue was thenpurified by silica gel column chromatography using ethylacetate/petroleum ether (20% EA in PE) to give the title compound.¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 7.55 (brs, 2H), 7.26 (d, J=3.6 Hz,1H), 6.60 (d, J=3.3 Hz, 1H), 6.31 (t, J=6.6 Hz, 1H), 4.55-4.50 (m, 1H),3.80-3.61 (m, 4H), 2.64-2.55 (m, 1H), 2.23-2.17 (m, 1H), 0.90-0.87 (m,18H), 0.11-0.06 (m, 12H). F-NMR: (282 MHz, d₆-DMSO, ppm): δ−53.64 (s,1F, β isomer), −53.78 (s, 1F, α isomer). LC-MS: (ES, m/z): 497.58[M+H]⁺.

Step 7:((2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol

To a stirred solution of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-4-amine(1.4 g, 2.82 mmol) in THF (24 mL) was added aqueous TFA (TFA/H₂O=1/1,v/v, 12 mL) dropwise with stirring at 0° C. in 10 minutes. The resultingmixture was allowed to stir at 0° C. The reaction progress was monitoredby TLC. After stirring for 5 hours, the started di-TBS protectednucleoside was all consumed, then the reaction mixture was co-evaporatedwith toluene (50 mL×3). The residue was re-dissolved in a mixture ofMeOH/DCM (15% MeOH in DCM, 50 mL). Solid NaHCO₃ (2 g) was added at 0°C., followed by the addition of water (1 mL). The resulting mixture wasstirred for 30 minutes. After the pH value was adjusted to 7, the solidswere filtered out, the filtrate was collected and concentrated underreduced pressure. The residue was purified by silica gel columnchromatography using ethyl acetate/petroleum ether (40% EA in PE) togive the title compound. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 7.57 (brs,2H), 7.32 (d, J=3.6 Hz, 1H), 6.61 (d, J=3.6 Hz, 1H), 6.32 (dd, J=6.0 Hz,J=8.0 Hz, 1H), 4.99-4.96 (m, 1H), 4.52 (t, J=2.8 Hz, 1H), 3.79 (q, J=2.4Hz, 1H), 3.54-3.49 (m, 2H), 2.57-2.53 (m, 1H), 2.19-2.13 (m, 1H),0.91-0.88 (m, 9H), 0.13-0.11 (m, 6H). F-NMR: (376 MHz, d₆-DMSO, ppm):δ−53.71 (s, 1F, β isomer), −53.89 (s, 1F, α isomer). LC-MS: (ES, m/z):383.36 [M+H]⁺.

Step 8: Synthesis of(2S,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde

TFA (0.051 mL, 0.659 mmol) was injected to a stirred solution of((2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol(360 mg, 0.941 mmol), DCC (N,N-dicyclohexylcarbodiimide) (602 mg, 2.92mmol) and pyridine (0.084 mL, 1.035 mmol) in anhydrous DMSO (2 mL) underargon atmosphere at room temperature in 2 min, and the mixture wasstirred overnight. The reaction progress was monitored by TLC & LCMS.The mixture was filtered to remove dicyclohexylurea, and the filtratewas partitioned with ethyl acetate (30 mL) and H₂O (30 mL). The organiclayer was collected and washed with brine (20 mL×2), dried overanhydrous Na₂SO₄, filtered and the filtrate was evaporated under reducedpressure to give the title compound, which was used to the next reactionstep directly without further purification. LC-MS: (ES, m/z): 381.20[M+H]⁺, 413.20 [M+MeOH+H]⁺.

Step 9: Synthesis of((3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol

To a stirred solution of(2S,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde(400 mg, 1.051 mmol) in 1,4-dioxane (8 mL) in a 50 mL round-bottomflask, was added formaldehyde solution (1.2 mL, 16.01 mmol), followed bythe addition of sodium hydroxide solution (1.2 mL, 2.400 mmol) dropwisein 2 minutes. The resulting mixture was stirred at 25° C. for 7 hours.Upon the started nucleoside was all consumed, the reaction mixture wasneutralized by addition of AcOH. The resulting mixture was diluted withAcOEt (100 mL) and washed successively with water (2×40 mL), saturatedaq NaHCO₃ (2×40 mL) and brine (50 mL). The organic layer was dried overNa₂SO₄ and evaporated under reduced pressure. The residue wasre-dissolved in EtOH (3 mL) and added sodium borohydride (199 mg, 5.26mmol) in portions at 0° C. After stirring for 5 hours at 25° C., thereaction mixture was neutralized by addition of AcOH. The mixture wasconcentrated under reduced pressure, the residue was partitioned betweenCHCl₃ (100 mL) and water (50 mL). The organic layer was washedsuccessively with water and brine, dried over Na₂SO₄, and evaporatedunder reduced pressure. The residue was purified by silica gel columnchromatography using dichloromethane/methanol (30/1) to give the titlecompound. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 7.55 (brs, 2H), 7.34 (d,J=3.6 Hz, 1H), 6.60 (d, J=3.6 Hz, 1H), 6.35 (t, J=7.0 Hz, 1H), 4.90 (t,J=3.6 Hz, 1H), 4.60 (q, J=2.8 Hz, 1H), 4.41 (t, J=3.6 Hz, 1H), 3.60-3.43(m, 4H), 2.69-2.62 (m, 1H), 2.23-2.17 (m, 1H), 0.92 (s, 9H), 0.09 (s,6H). F-NMR: (376 MHz, d₆-DMSO, ppm): δ−53.80 (s, 1F, β isomer). LC-MS:(ES, m/z): 413.32 [M+H]⁺, 435.34 [M+Na]⁺.

Step 10: Synthesis of(2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

To a stirred solution of((3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol(180 mg, 0.436 mmol) in anhydrous acetonitrile (15 mL) and dry DMSO (1.5mL) in a 50 mL round-bottom flask under argon atmosphere, was added IBX(367 mg, 1.309 mmol). The resulting mixture was stirred at 20° C. for 8hours. The reaction mixture was filtered, washed with dichloromethane.The filtrate was collected and concentrated under reduced pressure. Theresidue was re-dissolved in ethyl acetate (40 mL), washed with water(3×15 mL) and brine (2×20 mL) successively, dried over anhydrous Na₂SO₄,filtered and the filtrate was concentrated under reduced pressure togive the title compound, which was used to the next reaction stepdirectly without further purification. ¹H-NMR: (400 MHz, CDCl₃, ppm): δ9.65 (s, 1H), 7.60 (d, J=3.6 Hz, 1H), 6.43 (dd, J=5.6 Hz, J=9.6 Hz, 1H),6.39 (d, J=3.6 Hz, 1H), 5.56-5.43 (m, 3H), 4.96 (d, J=4.8 Hz, 1H), 4.08(d, J=11.2 Hz, 1H), 3.81 (d, J=12.8 Hz, 1H), 3.27-3.19 (m, 1H), 2.25(dd, J=5.4 Hz, J=13.0 Hz, 1H), 0.91 (s, 9H), 0.11 (d, J=5.2 Hz, 6H).

F-NMR: (376 MHz, CDCl₃, ppm): δ−53.14 (s, 1F). LC-MS: (ES, m/z): 411.21[M+H]⁺.

Step 11: Synthesis of((2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol

To a stirred solution of(2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(190 mg, 0.463 mmol) in anhydrous MeOH (8 mL) under argon atmosphere,was added potassium carbonate (160 mg, 1.157 mmol). The mixture wascooled to 0° C., then was added dimethyl(1-diazo-2-oxopropyl)phosphonate (178 mg, 0.926 mmol) dropwise in 1minute. The resulting mixture was warmed to 25° C. and stirredovernight. The reaction mixture was concentrated under reduced pressure,and then purified by silica gel column chromatography usingmethanol/dichloromethane (4.8% MeOH in DCM) to give the title compound.¹H-NMR: (400 MHz, CDCl₃, ppm): δ 6.99 (d, J=3.6 Hz, 1H), 6.35 (d, J=3.6Hz, 1H), 6.28 (dd, J=6.0 Hz, J=8.8 Hz, 1H), 5.45-5.33 (m, 3H), 4.76 (q,J=2.8 Hz, 1H), 4.03 (dd, J=2.0 Hz, J=12.4 Hz, 1H), 8.16-3.79 (m, 1H),3.12-3.06 (m, 1H), 2.70 (s, 1H), 2.33-2.27 (m, 1H), 0.94 (s, 9H), 0.16(d, J=8.0 Hz, 6H). F-NMR: (376 MHz, CDCl₃, ppm): δ−53.26 (s, 1F). LC-MS:(ES, m/z): 407.30 [M+H]⁺.

Step 12: Synthesis of(2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(9)

To a stirred solution of((2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(15 mg, 0.037 mmol) in anhydrous THF (1 mL) under argon atmosphere wasadded TBAF THF solution (0.037 mL, 0.037 mmol) dropwise with stirring in1 minute at ambient temperature. The medium was stirred at ambienttemperature for 2 hours. The reaction progress was monitored by TLC.Upon the started nucleoside was all consumed, the mixture wasconcentrated under vacuum, the residue was then purified bypreparative-TLC (MeOH/DCM=1/15) to give a crude product (10 mg). Thecrude product was further purified by preparative-HPLC with thefollowing conditions: (1#-Pre-HPLC-011 (Waters)): Column, X-bridge C18Column, 19*150 mm, 5 um; mobile phase, water with 10 mmol ammoniumbicarbonate and acetonitrile (5% acetonitrile up to 30% in 5 min, up to95% in 2 min); Detector, uv 254&220 nm. The product-containing fractionswere collected and lyophilized to give compound 9 as a solid. ¹H-NMR:(400 MHz, d₆-DMSO, ppm): δ7.57 (brs, 2H), 7.28 (d, J=3.6 Hz, 1H), 6.61(d, J=3.6 Hz, 1H), 6.35 (t, J=6.4 Hz, 1H), 5.51 (d, J=5.6 Hz, 1H), 5.27(t, J=6.0 Hz, 1H), 4.48 (dd, J=6.4 Hz, J=12.0 Hz, 1H), 3.61 (dd, J=5.6Hz, J=11.6 Hz, 1H), 3.53 (dd, J=6.4 Hz, J=12.0 Hz, 1H), 3.48 (s, 1H),2.50-2.46 (m, 1H), 2.37-2.31 (m, 1H). F-NMR: (376 MHz, d₆-DMSO, ppm):δ−53.67 (s, 1F). LC-MS: (ES, m/z): 293.15 [M+H]⁺, 315.15 [M+Na]⁺.

Example 10: Synthesis of(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-hydroxy-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile(10)

Step 1: Synthesis of5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehydeoxime

To a stirred solution of(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(Example 1, Intermediate C, 50 mg, 0.127 mmol, 1.0 eq) in dry pyridine(2.5 mL) was added hydroxylamine hydrochloride (26.6 mg, 0.382 mmol, 3.0eq) under argon atmosphere. The resulting mixture was stirred at 30° C.for 2 hours. The reaction progress was monitored by LCMS. The reactionmixture was concentrated under vacuum, the residue then dissolved inethyl acetate (50 mL), washed with water (2×30 mL) and brine (35 mL)successively, dried over anhydrous sodium sulfate, filtered and thefiltrate was concentrated under vacuum. The residue was purified bypreparative-TLC (DCM/MeOH=10/1) to afford the title compound. LC-MS:(ES, m/z): 408.20 [M+H]⁺.

Step 2: Synthesis of(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile

To a stirred mixture of5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehydeoxime (40 mg, 0.098 mmol) and triethylamine (105 mg, 1.038 mmol) in dryDCM (5 mL) was added 2,2,2-trifluoroacetic anhydride (110 mg, 0.524mmol) dropwise with stirring at 20° C. under argon atmosphere. Theresulting mixture was stirred at 20° C. for 20 hours. The reactionprogress was monitored by LCMS. The reaction mixture was diluted withDCM (30 mL), washed with saturated aqueous NaHCO₃ (25 mL) and brine (25mL) successively, dried over anhydrous Na₂SO₄, filtered and the filtratewas concentrated under vacuum. The residue was purified bypreparative-TLC (DCM/MeOH=10/1) to afford the title compound. LC-MS:(ES, m/z): 390.11 [M+H]⁺. ¹H-NMR: (300 MHz, CD3OD, ppm): δ 8.10 (s, 1H),7.30 (d, J=3.6 Hz, 1H), 6.68 (t, J=6.9 Hz, 1H), 6.64 (d, J=3.6 Hz, 1H),4.90 (t, J=6.3 Hz, 1H), 3.85 (dd, J=12.0 Hz, J=21.6 Hz, 2H), 2.85-2.94(m, 1H), 2.42-2.49 (m, 1H), 1.02 (s, 9H), 0.26 (d, J=9.0 Hz, 6H).

Step 3: Synthesis of(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-hydroxy-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile(10)

To a stirred solution of(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile(35 mg, 0.090 mmol) in dry THF (5 mL) was added TBAF THF solution (1.0M, 0.108 mL, 0.108 mmol) dropwise with stirring under argon atmosphereat 15° C. The resulting mixture was stirred at 15° C. for 0.5 hours. Thereaction progress was monitored by LCMS and TLC. The reaction mixturewas concentrated under vacuum. The residue was purified bypreparative-TLC (DCM/MeOH=10/1) to give a syrup. The crude product wasfurther purified by Prep-HPLC with the following conditions:(1#-Pre-HPLC-011 (Waters)): Column, SunFire C18 reverse Column, 19*150mm, 5 um; mobile phase, water with 10 mmol ammonium bicarbonate andacetonitrile (5% acetonitrile up to 20% in 7.5 min, up to 95% in 2 min,down to 5% in 1 min); Detector, uv 254&220 nm. The product-containingfractions were collected and lyophilized to give the title compound 10as a solid. LC-MS: (ES, m/z): 276.10 [M+H]⁺. ¹H-NMR: (400 MHz, d₆-DMSO,ppm): δ 8.07 (s, 1H), 7.34 (d, J=3.6 Hz, 1H), 7.33 (br, 2H), 7.08 (s,1H), 6.64 (t, J=7.0 Hz, 1H), 6.61 (d, J=3.6 Hz, 1H), 6.27 (d, J=4.8 Hz,1H), 5.82 (t, J=6.0 Hz, 1H), 4.61 (dd, J=4.8 Hz, J=10.0 Hz, 1H), 3.75(dd, J=5.6 Hz, J=12.0 Hz, 1H), 3.62 (dd, J=6.0 Hz, J=11.6 Hz, 1H),2.74-2.81 (m, 1H), 2.33-2.38 (m, 1H).

Example 11: Synthesis of(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(11)

Step 1: Synthesis of 4-(methylthio)pyrrolo[2,1-f][1,2,4]triazine

The synthesis of 4-chloropyrrolo[2,1-f][1,2,4]triazine is described inWO2011/150356A1, 2011. Into a 500-mL round-bottom flask, was placed asolution of 4-chloropyrrolo[2,1-f][1,2,4]triazine (17 g, 110.70 mmol)and (methylsulfanyl)sodium (15 g, 214.01 mmol. in tetrahydrofuran (300mL). The resulting solution was stirred for 1 overnight at roomtemperature. The solids were filtered out. The resulting mixture wasconcentrated in vacuo. The residue was applied onto a silica gel columnwith ethyl acetate/petroleum ether (1:10). This resulted in the titlecompound. LC-MS (ES, m/z): 166 [M+H]⁺

Step 2:(3R,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)-2-(4-(methylthio)pyrrolo[2,1-f][1,2,4]triazin-7-yl)tetrahydrofuran-2-ol

To a solution of 4-(methylthio)pyrrolo[2,1-f][1,2,4]triazine (1.650 g,9.99 mmol) in THF (30 mL) was added lithium diisopropylamide (7.5 mL,15.00 mmol) at −78° C. under argon atmosphere and the resulting mixturewas stirred for 30 minutes at −78° C. After that,(3R,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)dihydrofuran-2(3H)-one(4.18 g, 9.99 mmol) in THF (10 mL) was added at −78° C. under argonatmosphere and stirred 120 minutes at −78 to −50° C. The reaction wasquenched by additional of ammonium chloride (aq, 10 mL), and thenextracted with ethyl acetate (300 mL). The organic layer was washed with(3×50 mL) brine, dried over sodium sulfate and concentrated undervacuum. The residue was applied on a silica gel column, eluted withethyl acetate/petroleum ether (1:5) to give the title compound. LC-MS:584.2 [M+H]⁺

Step 3: Synthesis of7-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-4-(methylthio)pyrrolo[2,1-f][1,2,4]triazine

To a solution of3R,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)-2-(4-(methylthio)pyrrolo[2,1-f][1,2,4]triazin-7-yl)tetrahydrofuran-2-ol(3.00 g, 5.14 mmol) in DCM (30 mL) was added triethylsilane (2.390 g,20.56 mmol) and trifluoroborane (0.697 g, 10.28 mmol) at 0° C. underargon atmosphere. The resulting solution was stirred for 30 minutes at0° C. and then quenched by additional of sodium bicarbonate (aq, 20 mL),extracted by DCM (200 mL). The organic layer was washed with 3×50 mLbrine, dried over sodium sulfate and concentrated under vacuum. Theresidue was applied on a silica gel column, eluted with ethylacetate/petroleum ether (1:10) to give the title compound. LC-MS: 568.4[M+H]⁺. ¹H-NMR: (300 MHz, CDCl₃, ppm): δ 8.21 (s, 1H), 7.23-7.36 (m,15H), 6.81 (d, J=4.5 Hz, 1H), 6.70 (d, J=4.5 Hz, 1H), 5.69 (d, J=4.2 Hz,1H), 4.37-4.62 (m, 7H), 4.22-4.26 (m, 1H), 4.10-4.13 (m, 1H), 3.66-3.67(m, 1H), 3.62-3.63 (m, 1H), 2.75 (s, 3H).

Step 4: Synthesis of7-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)pyrrolo[2,1-f][1,2,4]triazin-4-amine

To a solution of7-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-4-(methylthio)pyrrolo[2,1-f][1,2,4]triazine(4.6 g, 8.10 mmol) in 2-propanol (5 mL) was flushed ammonia (1350 mg, 79mmol) at −40° C. for 60 minutes in sealed tube. After the resultingmixture was stirred for 16 hours at 80° C., it was evaporated to givethe title compound. LC-MS: 537.3 [M+H]⁺. ¹H-NMR: (300 MHz, DMSO, ppm): δ7.80 (s, 1H), 7.69 (s, 2H), 7.24-7.36 (m, 15H), 6.88 (d, J=4.5 Hz, 1H),6.80 (d, J=4.2 Hz, 1H), 5.44 (d, J=5.4 Hz, 1H), 4.49-4.62 (m, 6H), 4.31(t, J=5.1 Hz, 1H), 4.15-4.18 (m, 1H), 4.09-4.12 (m, 1H), 3.29-3.67 (m,2H).

Step 5: Synthesis of(2S,3R,4S,5R)-2-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-(hydroxymethyl)tetrahydrofuran-3,4-diol

To a solution of7-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)pyrrolo[2,1-f][1,2,4]triazin-4-amine(100 mg, 0.186 mmol) in acetic acid (2 mL) was added Pd(OH)₂ (10 mol%)/C (100 mg, 0.130 mmol) under hydrogen at 25° C. for 4 hours. Themixture was filtered through a celite pad, and the filtrate wasevaporated. The residue was applied on a silica gel column, eluted withMeOH/DCM (1:8) to give the title compound. LC-MS: 267.2 [M+H]⁺. ¹H-NMR:(300 MHz, DMSO, ppm): δ 7.79 (s, 1H), 7.77 (s, 2H), 6.84 (d, J=4.2 Hz,1H), 6.68 (d, J=4.2 Hz, 1H), 5.10 (d, J=6.6 Hz, 1H), 4.95 (d, J=6.6 Hz,1H), 4.84 (d, J=4.8 Hz, 1H), 4.76 (t, J=5.4 Hz, 1H), 4.20-4.25 (m, 1H),3.94 (d, J=4.8 Hz, 1H), 3.78 (d, J=4.2 Hz, 1H), 3.41-3.64 (m, 2H).

Step 6: Synthesis of(6aR,8S,9S,9aS)-8-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-ol

(2S,3R,4S,5R)-2-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-5-(hydroxymethyl)tetrahydrofuran-3,4-diol(790 mg, 2.97 mmol) and 1H-imidazole (606 mg, 8.90 mmol) were dissolvedin DMF (20 mL) under argon.1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane (936 mg, 2.97 mmol) wasadded by dropwise at 0° C. After the resulting mixture was stirred for 5hours at 25° C. under argon, water (10 mL) was added and the resultingmixture was diluted with ethyl acetate (400 mL). The organic phase waswashed with (3×60 mL) of water and 60 mL of brine, dried over Na₂SO₄ andconcentrated under vacuum. The residue was applied on a silica gel,eluted with MeOH/DCM (1:20) to give the title compound. LC-MS: 509.3[M+H]⁺. ¹H-NMR: (400 MHz, DMSO, ppm): δ 7.81 (s, 1H), 7.70 (s, 2H), 6.82(d, J=4.8 Hz, 1H), 6.61 (d, J=4.4 Hz, 1H), 5.20 (d, J=4.8 Hz, 1H), 5.16(d, J=1.6 Hz, 1H), 4.31-4.35 (m, 1H), 4.12-4.15 (m, 1H), 4.00-4.03 (m,1H), 3.88-3.91 (m, 1H), 0.96-1.05 (m, 28H)

Step 7: Synthesis ofO-((6aR,8S,9S,9aR)-8-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-yl)O-phenylcarbonothioate

(6aR,8S,9S,9aS)-8-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-ol(210 mg, 0.413 mmol) and N,N-dimethylpyridin-4-amine (202 mg, 1.651mmol) were dissolved in DCM (10 mL) under argon. O-phenylcarbonochloridothioate (143 mg, 0.826 mmol) were added by dropwise at 0°C. After the reaction was stirred at 25° C. under argon for 2 hours, theresulting mixture was diluted with DCM (100 mL), and then washed with3×30 mL of water and 30 mL of brine. The organic layer was dried overNa₂SO₄ and concentrated under vacuum. The residue was applied on asilica gel column and eluted with ethyl acetate/petroleum ether (3:1) togive the title compound. LC-MS: 645.2 [M+H]⁺, ¹H-NMR: (400 MHz, DMSO,ppm): δ 7.83 (s, 2H), 7.79 (s, 1H), 7.48 (t, J=8.0 Hz, 2H), 7.33 (t,J=7.2 Hz, 1H), 7.14 (d, J=7.6 Hz, 2H), 6.80 (d, J=4.4 Hz, 1H), 6.71 (d,J=4.4 Hz, 1H), 6.16 (dd, J=2.4 Hz, J=5.6 Hz, 1H), 5.46 (d, J=2.0 Hz,1H), 4.90 (dd, J=5.6 Hz, J=8.8 Hz, 1H), 3.95-4.06 (m, 2H), 3.85-3.87 (m,1H), 0.96-1.06 (m, 28H).

Step 8: Synthesis of7-((6aR,8R,9aS)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-8-yl)pyrrolo[2,1-f][1,2,4]triazin-4-amine

O-((6aR,8S,9S,9aR)-8-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-yl)O-phenylcarbonothioate (1.45 g, 2.248 mmol), AIBN (0.738 g, 4.50 mmol) andtributylstannane (3.93 g, 13.49 mmol) were dissolved in toluene (20 mL)under argon. After the reaction was stirred at 80° C. under argon for 3hours, the resulting solution was concentrated under vacuum. The residuewas applied on a silica gel column and eluted with ethylacetate/petroleum ether (2.5:1) to give the title compound. LC-MS: 493.4[M+H]⁺, ¹H-NMR: (400 MHz, DMSO, ppm): δ 7.81 (s, 1H), 7.79 (s, 2H), 6.81(d, J=4.4 Hz, 1H), 6.60 (d, J=4.4 Hz, 1H), 5.46 (t, 1H), 4.58-4.62 (m,1H), 3.90-4.00 (m, 1H), 3.75-3.80 (m, 2H), 2.20-2.30 (m, 1H), 2.30-2.40(m, 1H), 0.98-1.06 (m, 28H).

Step 9: Synthesis of(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

7-((6aR,8R,9aS)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-8-yl)pyrrolo[2,1-f][1,2,4]triazin-4-amine(1.0 g, 2.029 mmol) was dissolved in THF (10 mL) under argon. TBAF(0.531 g, 2.029 mmol) was added to the reaction solution by dropwise at20° C. After the resulting solution was stirred at 20° C. under argonfor 2 hours, it was concentrated under vacuum. The residue was appliedon a silica gel column and eluted with DCM/MeOH (20:1) to give the titlecompound. LC-MS: 251.2 [M+H]⁺, ¹H-NMR: (400 MHz, DMSO, ppm): δ7.83 (s,1H), 7.81 (s, 2H), 6.84 (d, J=4.8 Hz, 1H), 6.82 (d, J=4.4 Hz, 1H),5.47-5.51 (m, 1H), 5.06 (d, J=4.0 Hz, 1H), 4.73 (t, J=6.0 Hz, 1H), 4.22(m, 1H), 3.74-3.78 (m, 1H), 3.32-3.45 (m, 2H), 2.16-2.20 (m, 1H),2.09-2.14 (m, 1H).

Step 10: Synthesis of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)pyrrolo[2,1-f][1,2,4]triazin-4-amine

(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(300 mg, 1.199 mmol), 1H-imidazole (490 mg, 7.19 mmol) andtert-butylchlorodimethylsilane (723 mg, 4.80 mmol) were dissolved in DMF(4.0 mL) under argon. After the reaction mixture was stirred at 20° C.under argon for 5 hours, the resulting mixture was diluted with ethylacetate (100 mL), washed with (3×30 mL) of water and 30 mL of brine. Theorganic layer was dried with Na₂SO₄ and concentrated under vacuum. Theresidue was applied on a silica gel column and eluted with ethylacetate/petroleum ether (2:1) to give the title compound. LC-MS: 479.3[M+H]⁺, ¹H-NMR: (300 MHz, DMSO, ppm): δ 7.82 (s, 1H), 7.75 (s, 2H), 6.82(d, J=4.5 Hz, 1H), 6.61 (d, J=4.5 Hz, 1H), 5.48-5.53 (m, 1H), 4.42 (m,1H), 3.78 (m, 1H), 3.48-3.62 (m, 2H), 2.22-2.27 (m, 1H), 2.04-2.10 (m,1H), 0.78-0.89 (m, 18H), 0.00-0.10 (m, 12H)

Step 11: Synthesis of((2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol

7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)pyrrolo[2,1-f][1,2,4]triazin-4-amine (500 mg, 1.044 mmol) was dissolved in THF(8.0 mL), H₂O (2.0 mL) and TFA (2.0 mL) and stirred at 0° C. for 4hours. The reaction mixture was adjusted to pH 7 with sodium bicarbonateand then extracted with ethyl acetate (30 mL×3), washed with (3×20 mL)of water and 20 mL of brine. The organic layer was dried over Na₂SO₄ andconcentrated under vacuum. The residue was applied on a silica gelcolumn and eluted with ethyl acetate/petroleum ether (2:1) to give thetitle compound. LC-MS: 365.3 [M+H]⁺, ¹H-NMR: (400 MHz, DMSO, ppm): δ7.82 (s, 1H), 7.68 (s, 2H), 6.82 (d, J=4.4 Hz, 1H), 6.65 (d, J=4.4 Hz,1H), 5.46-5.50 (m, 1H), 4.80 (t, J=5.6 Hz, 1H), 4.42 (d, J=4.2 Hz, 1H),3.74-3.78 (m, 1H), 3.32-3.44 (m, 2H), 2.24-2.28 (m, 1H), 2.02-2.06 (m,1H), 0.85-0.90 (m, 9H), 0.00-0.10 (m, 6H).

Step 12: Synthesis of(2S,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde

((2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol(270 mg, 0.741 mmol) and IBX (270 mg, 0.963 mmol) was dissolved inacetonitrile (20.0 mL) under argon. After the reaction mixture wasstirred at 80° C. under argon for 1 hour, the solid was filtered out andthe filtrate was concentrated under vacuum to give the title compoundwhich was used for next step directly. LC-MS: 363.2 [M+H]⁺, ¹H-NMR: (400MHz, DMSO, ppm): δ 9.59 (s, 1H), 7.84 (s, 1H), 7.73 (s, 2H), 6.86 (d,J=4.4 Hz, 1H), 6.64 (d, J=4.4 Hz, 1H), 5.67-5.71 (m, 1H), 4.71 (d, J=4.4Hz, 1H), 4.25 (s, 1H), 2.25-2.32 (m, 1H), 2.12-2.17 (m, 2H), 0.84-0.91(m, 9H), 0.00-0.13 (m, 6H).

Step 13: Synthesis of((3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol

(2S,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde(200 mg, 0.552 mmol) was dissolved in 1,4-dioxane (10 mL) at 20° C. Thenformaldehyde (2.0 mL, 0.552 mmol) and sodium hydroxide (2.0 mL, 4.00mmol) were added. After the resulting mixture was stirred at 20° C. for4 hours, it was adjusted to pH 7 with acetic acid. The mixture wasdiluted with ethyl acetate (150 mL), then washed with 3×30 mL of waterand 30 mL of brine. The organic layer was dried over Na₂SO₄, andconcentrated under vacuum. The residue was dissolved in ethanol (10 mL)at 0° C., and then NaBH₄ (41.7 mg, 1.103 mmol) was added at 0° C. Afterthe resulting mixture was stirred at 20° C. for 16 hours, it wasadjusted to pH=7 with acetic acid and the mixture was extracted withethyl acetate (150 mL), then washed with (3×30 mL) of water and 30 mL ofbrine. The organic layer was dried over Na₂SO₄ and concentrated undervacuum. The residue was applied to a silica gel column and eluted withDCM/MeOH (10:1) to give the title compound. LC-MS: 395.2 [M+H]⁺, ¹H-NMR:(400 MHz, DMSO, ppm): δ7.82 (s, 1H), 7.70 (s, 2H), 6.82 (d, J=4.4 Hz,1H), 6.66 (d, J=4.4 Hz, 1H), 5.50-5.60 (m, 1H), 4.68 (t, 1H), 4.52 (d,J=4.4 Hz, 1H), 4.22 (t, 1H), 3.53-3.60 (m, 2H), 2.35-2.45 (m, 1H),2.00-2.10 (m, 1H), 0.90 (s, 9H), 0.08-0.09 (m, 6H).

Step 14: Synthesis of(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

((3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol(90 mg, 0.228 mmol) and IBX (256 mg, 0.912 mmol) were dissolved inacetonitrile (15.0 mL) under argon. After the reaction mixture wasstirred at 30° C. under argon for 48 hours, the solid was filtered out.The filtrate was concentrated under vacuum to give the title compound,which was used for next step directly.

Step 15: Synthesis of((2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol

(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(80 mg, 0.204 mmol) and K₂CO₃ (85 mg, 0.611 mmol) were dissolved inmethanol (10 mL) under argon. Dimethyl (1-diazo-2-oxopropyl)phosphonate(78 mg, 0.408 mmol) was added to the reaction mixture dropwise at 0° C.After the reaction mixture was stirred at 25° C. under argon for 16hours, it was filtrated and concentrated under vacuum. The residue wasapplied to a silica gel column and eluted with DCM/MeOH (10:1) to givethe title compound. LC-MS: 389.3 [M+H]⁺

Step 16: Synthesis of(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(11)

((2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(50 mg, 0.129 mmol) and TBAF (33.6 mg, 0.129 mmol) were dissolved in THF(5.0 mL) under argon. After the resulting solution was stirred at 25° C.under argon for 2 hours, the reaction mixture was concentrated undervacuum. The residue was purified by Prep-HPLC with the followingconditions (1#-Pre-HPLC-011 (Waters)): Column, Xbridge Prep C18 Column,19*150 mm; mobile phase, water (10 mmoL/L NH₄HCO₃) and acetonitrile(5.0% acetonitrile up to 25.0% in 8 min, up to 95.0% in 1.5 min, down to5.0% in 1.5 min); Detector, UV254 & 220 nm) to give the title compound11 as a solid. LC-MS: 275.1 [M+H]⁺, ¹H-NMR: (400 MHz, DMSO, ppm): δ7.82(s, 1H), 7.69 (s, 2H), 6.82 (d, J=4.4 Hz, 1H), 6.69 (d, J=4.0 Hz, 1H),5.60 (t, J=7.6 Hz, 1H), 5.28 (d, J=4.2 Hz, 1H), 5.06 (d, J=6.8 Hz, J=6.0Hz, 1H), 4.30-4.34 (m, 1H), 3.45-3.56 (m, 2H), 3.38 (s, 1H), 2.30-2.37(m, 1H), 2.17-2.13 (m, 1H).

Example 12: Synthesis of(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-hydroxy-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile(12)

Step 1: Synthesis of5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehydeoxime

To a mixture of Intermediate D (see Example 11) (70 mg, 0.178 mmol) inpyridine (5 mL) under argon was added hydroxylamine hydrochloride (37.17mg, 0.543 mmol) at 25° C. After the resulting mixture was stirred for 2hours at 25° C., the reaction mixture was concentrated under reducedpressure. The residue was diluted with ethyl acetate (100 mL), washedwith water (3×20 mL) and brine (20 mL), dried over anhydrous sodiumsulfate and concentrated under reduced pressure to afford the titlecompound that was used without purification. LC-MS: 408.2 [M+H]⁺

Step 2: Synthesis of(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile

To a mixture of5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehydeoxime (70 mg, 0.172 mmol) in DCM (15 mL) under argon was added Et₃N(69.5 mg, 0.687 mmol) and 2,2,2-trifluoroacetic anhydride (72.2 mg,0.344 mmol) at 25° C. The resulting mixture was stirred for 16 hours at25° C. and then the reaction mixture was diluted with DCM (100 mL),washed with sat aqueous sodium bicarbonate (3×20 mL) and brine (20 mL),dried over anhydrous sodium sulfate and concentrated under reducedpressure. The residue was purified by a silica gel column, eluting withDCM/MeOH (15:1) to afford the title compound. LC-MS: 309.2 [M+H]⁺.

Step 3: Synthesis of(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-hydroxy-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile(12)

To a mixture of(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile(50 mg, 0.128 mmol) in THF (10 mL) under argon was added TBAF (33.6 mg,0.128 mmol) at 25° C. The resulting mixture was stirred for 2 hours at25° C. and then concentrated under reduced pressure. The crude productwas purified by Prep-HPLC with the following conditions: Instrument,(1#-Pre-HPLC-011 (waters)); Column: Xbridge C18, 5 um, 19×150 mm; mobilephase: water (0.05% NH₄CO₃) and ACN (5.0% ACN up to 40% in 10 min, hold95% for 2 minutes, down to 5% in 2 minutes); Detector, UV 220 and 254nm. The collected fractions were combined and concentrated underreducing pressure to give the title compound 12 as a solid. LC-MS: 276.0[M+H]⁺, ¹H-NMR: (400 MHz, DMSO, ppm): δ7.86 (s, 1H), 7.74-7.84 (s, 2H),6.88 (d, J=4.4 Hz, 1H), 6.84 (d, J=4.4 Hz, 1H), 6.10 (d, J=4.4 Hz, 1H),5.72-5.79 (m, 1H), 5.62-5.63 (m, 1H), 4.44-4.61 (s, 1H), 3.53-3.62 (m,2H), 2.42-2.49 (m, 1H), 2.19-2.24 (m, 1H).

Example 13: ammonium((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltriphosphate (13)

Step1:2-((4,4,6,6-tetraoxido-1,3,5,2,4,6-trioxatriphosphinan-2-yl)oxy)benzoate(Intermediate E)

In a glove box under an argon atmosphere, dry tributylamine (0.4 mL,1.679 mmol) was added to the flask containing tributylammoniumpyrophosphate (112 mg, 0.205 mmol) dissolved in 0.4 mL dimethylformamide(DMF) to give a clear solution. The clear solution was then injectedinto the flask containing dry2-chloro-4H-benzo[d][1,3,2]dioxaphosphinin-4-one (27.6 mg, 0.136 mmol)in dimethylformamide (0.4 mL) under vigorous stirring. The resultingmixture was stirred at 30° C. for 30 minutes to give a solution ofIntermediate E which was used to the next reaction directly without anywork-up.

Step 2: Synthesis of ammonium((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltriphosphate (13)

(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol (Compound 1, 8 mg, 0.029 mmol) was placed into around-bottom flask (10 mL) and then dried over P₂O₅ under high vacuumovernight. To this flask was added activated molecular sieves 4A (100mg). The medium was charged with argon and then a solution ofIntermediate E (2.0 eq, freshly prepared) in dry DMF (0.15 mL) wastransferred into the above flask by syringes and the mixture was stirredat 25° C. for 3 hours. The reaction progress was monitored by TLC(acetonitrile:0.1 M ammonium chloride=7:3). Upon most of the startednucleoside was consumed, the mixture was cooled down to 0° C., iodinesolution [3% in 0.1 mL of pyridine/water (9:1)] was then injected intothe reaction mixture. As the iodine was consumed, dropwise addition ofthe iodine solution was continued until a permanent brown color ofiodine was maintained. After 15 minutes, triethylammonium bicarbonatebuffer (1.0 M, 2 mL) was added with stirring at 10° C. for another 15minutes. The volatile was removed under vacuum (inner temperature notexceed 25° C.). The residue was re-dissolved in water (2 mL) andextracted with chloroform (2×2 mL). The collected aqueous layer whichcontaining crude product was then purified by preparative-HPLC with thefollowing conditions (1#-Pre-HPLC-011 (Waters)): Column, XBridge™ PrepOBD (Optimum Bed Density) T3 Column, 19*150 mm, 5 um; mobile phase,water with 50 mmol ammonium bicarbonate and acetonitrile (2%acetonitrile up to 5.2% in 5 min, up to 95% in 2 min, down to 5% in 1.5min); Detector, UV 254 & 220 nm. The product-containing fractions werecollected and lyophilized to give the title compound 13 as a solid.LC-MS: (ES, m/z): 512.90 [M−H−4NH₃]⁻. ¹H-NMR: (400 MHz, D₂O, ppm): δ8.06 (s, 1H), 7.38 (d, J=3.6 Hz, 1H), 6.63 (t, J=7.6 Hz, 1H), 6.58 (d,J=3.6 Hz, 1H), 4.06-4.14 (m, 2H), 2.67-2.72 (m, 1H), 2.54-2.59 (m, 1H).P-NMR: (161 MHz, D₂O, ppm): δ −5.86 (s, 1P), −11.49-11.39 (d, J=15.13Hz, 1P), −19.29 (s, 1P).

The following compounds 14-21 were synthesized using the methoddescribed in Example 13:

Example 14: ammonium((2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltriphosphate (14)

LC-MS: (ES, m/z): 530.85 [M−H−4NH₃]⁻. ¹H-NMR: (400 MHz, D₂O, ppm): δ8.00 (s, 1H), 7.14 (s, 1H), 6.62 (dd, J=4.8 Hz, J=6.0 Hz, 1H), 4.13 (dd,J=5.6 Hz, J=11.2 Hz, 1H), 4.06 (dd, J=5.0 Hz, J=11.4 Hz, 1H), 2.48-2.64(m, 2H). P-NMR: (161 MHz, D₂O, ppm): δ−5.97-5.89 (d, J=13.85 Hz, 1P),−11.52-11.43 (d, J=14.81 Hz, 1P), −19.31 (s, 1P).

Example 15: ammonium(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltriphosphate (15)

LC-MS: (ES, m/z): 527.00 [M−H−4NH₃]⁻. ¹H-NMR: (400 MHz, D₂O, ppm): δ7.96 (s, 1H), 7.07 (s, 1H), 6.55 (t, J=6.6 Hz, 1H), 4.11 (dd, J=6.2 Hz,J=11.4 Hz, 1H), 4.05 (dd, J=5.8 Hz, J=12.0 Hz, 1H), 2.59-2.66 (m, 1H),2.48-2.53 (m, 1H), 2.78 (s, 3H). P-NMR: (161 MHz, D₂O, ppm): δ−5.90 (s,1P), −11.48-11.39 (d, J=14.49 Hz, 1P), −19.32 (s, 1P).

Example 16: bis-triethylammonium((2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltriphosphate (16)

LC-MS: (ES, m/z): 546.95 [M−H−2TEA]⁻. ¹H-NMR: (400 MHz, D₂O, ppm): δ7.31 (d, J=4.0 Hz, 1H), 6.53 (d, J=4.0 Hz, 1H), 6.50 (t, J=6.4 Hz, 1H),4.15 (dd, J=5.8 Hz, J=10.6 Hz, 1H), 4.08 (dd, J=4.8 Hz, J=11.2 Hz, 1H),2.62-2.67 (m, 1H), 2.53-2.58 (m, 1H). P-NMR: (161 MHz, D₂O, ppm):δ−5.86-5.77 (d, J=14.81 Hz, 1P), −11.45-11.35 (d, J=15.13 Hz, 1P),−19.24 (s, 1P).

Example 17: ammonium((2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltriphosphate (17)

LC-MS: (ES, m/z): 546.70 [M−H−4NH₃]⁻. ¹H-NMR: (400 MHz, D₂O, ppm): δ7.97 (s, 1H), 7.34 (s, 1H), 6.54 (t, J=6.0 Hz, 1H), 4.01-4.13 (m, 2H),2.52-2.62 (m, 2H). P-NMR: (161 MHz, D₂O, ppm): δ−5.81 (s, 1P), −11.42(s, 1P), −19.25 (s, 1P).

Example 18: bis-triethylammonium((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-cyano-3-hydroxytetrahydrofuran-2-yl)methyltriphosphate (18)

LC-MS: (ES, m/z): 514.35 [M−H−2TEA]⁻. ¹H-NMR: (400 MHz, D₂O, ppm): δ8.04 (s, 1H), 7.29 (d, J=3.2 Hz, 1H), 6.70 (t, J=6.8 Hz, 1H), 6.55 (d,J=3.2 Hz, 1H), 4.87 (t, J=6.0 Hz, 1H), 4.21-4.16 (m, 2H), 2.99 (q, J=7.2Hz, 15H), 2.80-2.76 (m, 1H), 2.58-2.54 (m, 1H), 1.12 (t, J=7.2 Hz, 26H).P-NMR: (161 MHz, D₂O, ppm): δ−5.85 (s, 1P), −11.84 (d, J=15.30 Hz, 1P),−19.38 (s, 1P).

Example 19: ammonium((2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltriphosphate (19)

LC-MS: (ES, m/z): 512.90 [M−H−4NH₃]⁻. ¹H-NMR: (400 MHz, D₂O, ppm): δ7.73 (s, 1H), 6.77 (dd, J=4.4 Hz, J=7.4 Hz, 2H), 5.73 (t, J=7.4 Hz, 1H),4.52-4.56 (m, 1H), 3.98-4.03 (m, 2H), 2.56-2.63 (m, 1H), 2.34-2.40 (m,1H). P-NMR: (161 MHz, D₂O, ppm): δ−5.79 (s, 1P), −11.24 (s, 1P), −19.21(s, 1P).

Example 20: ammonium((2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltriphosphate (20)

LC-MS: (ES, m/z): 513.95 [M−H−4 NH₃]⁻. ¹H-NMR: (400 MHz, D₂O, ppm): δ8.22 (s, 1H), 7.99 (s, 1H), 5.53 (t, J=7.6 Hz, 1H), 4.60-4.57 (m, 1H),4.12-4.03 (m, 2H), 2.56-2.49 (m, 1H), 2.35-2.29 (m, 1H). P-NMR: (161MHz, D₂O, ppm): δ−5.82 (s, 1P), −11.32-11.23 (d, J=13.69 Hz, 1P), −19.24(s, 1P).

Example 21: ammonium((2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltriphosphate (21)

LC-MS: (ES, m/z): 513.95 [M−H−4NH₃]⁻. ¹H-NMR: (400 MHz, D₂O, ppm): δ8.23 (s, 1H), 7.98 (s, 1H), 5.66 (t, J=7.6 Hz, 1H), 4.61-4.58 (m, 1H),4.05 (brs, 2H), 2.68-2.61 (m, 1H), 2.46-2.42 (m, 1H). P-NMR: (161 MHz,D₂O, ppm): δ−5.81 (s, 1P), −11.33-11.24 (d, J=13.85 Hz, 1P), −19.19 (s,1P).

The names of the corresponding salt-free form of compounds 13-21 are,respectively:

-   13)    ((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyl    tetrahydrogen triphosphate;-   14)    ((2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyl    tetrahydrogen triphosphate;-   15)    ((2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyl    tetrahydrogen triphosphate;-   16)    ((2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyl    tetrahydrogen triphosphate;-   17)    ((2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyl    tetrahydrogen triphosphate;-   18)    ((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-cyano-3-hydroxytetrahydrofuran-2-yl)methyl    tetrahydrogen triphosphate;-   19) ((2R,3S,5R)-5-(4-aminopyrrolo[2,    1-f][1,2,4]triazin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyl    tetrahydrogen triphosphate;-   20)    ((2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyl    tetrahydrogen triphosphate; and-   21)    ((2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyl    tetrahydrogen triphosphate.

Example 22: Synthesis of(2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(22)

Step 1: Synthesis of (aminooxy)diphenylphosphine oxide

To a stirred solution of hydroxylamine hydrochloride (70 g, 1007 mmol)in a mixture of 1,4-dioxane (100 mL) and water (100 mL) was added asolution of NaOH (38.3 g, 957 mmol) in water (400 mL) dropwise withstirring at 0° C. in 30 minutes. The resulting solution was stirred at0° C. for 20 minutes. To the above was injected a solution ofdiphenylphosphinic chloride (77 mL, 403 mmol) in 1,4-dioxane (100 mL)quickly at 0° C. The resulting mixture was stirred vigorously at ambienttemperature for 10 minutes. A precipitate was formed and collected byfiltration. The solid was re-suspended in aq NaOH (0.25 N, 1000 mL) andstirred at 4° C. for 1.5 hours. The mixture was filtered and the filtercake was washed with water (3×1000 mL) and ether (2×500 mL)successively. The solid was dried under vacuum overnight to give(aminooxy)diphenylphosphine oxide. LC-MS: (ES, m/z): 233.9 [M+H]⁺.¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 7.82-7.69 (m, 4H), 7.58-7.40 (m, 6H)P-NMR: (121 MHz, d₆-DMSO, ppm): δ 21.53 (s, 1P).

Step 2: Synthesis of ethyl 1-amino-1H-imidazole-2-carboxylate

To a stirred solution of ethyl 1H-imidazole-2-carboxylate (6 g, 30.9mmol) in DMF (250 mL) under argon atmosphere was added LiHMDS THFsolution (93 mL, 93 mmol, 1 M) dropwise at −10° C. for 60 minutes. Theresulting mixture was stirred at −10° C. for additional 30 min, and then(aminooxy)diphenylphosphine oxide (21.63 g, 93 mmol) was added inportions for 30 minutes while maintained the temperature between 0° C.to 10° C. The resulting mixture was warmed to room temperature andstirred vigorously for 16 hours. The reaction was quenched with icewater (600 mL) and extracted with EtOAc (2×800 mL). The combined organiclayers was dried over anhydrous Na₂SO₄, filtered and the filtrate wasconcentrated under reduced pressure to give ethyl1-amino-1H-imidazole-2-carboxylate which was used for the next reactionstep directly without further purification. LC-MS: (ES, m/z): 156.1[M+H]⁺. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 7.37 (d, J=0.8 Hz, 1H), 6.96(d, J=0.8 Hz, 1H), 6.57 (br s, 2H), 4.33-4.27 (m, 2H), 1.31 (t, J=7.2Hz, 3H).

Step 3: Synthesis of imidazo[2,1-f][1,2,4]triazin-4(3H)-one

To a stirred mixture of ethyl 1-amino-1H-imidazole-2-carboxylate (6 g,30.9 mmol) in EtOH (60 mL) under argon atmosphere was added formamidineacetate (17.71 g, 170 mmol). The resulting mixture was heated to refluxand stirred overnight. The reaction mixture was cooled to ambienttemperature and filtered. The filter cake was washed with water (3×10mL) and EtOAc (2×10 mL) successively. The collected solid was driedunder high vacuum overnight to giveimidazo[2,1-f][1,2,4]triazin-4(3H)-one. LC-MS: (ES, m/z): 136.9 [M+H]⁺.¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 12.31 (br s, 1H), 8.09 (s, 1H), 7.98(d, J=0.8 Hz, 1H), 7.50 (d, J=0.8 Hz, 1H).

Step 4: Synthesis of 4-chloroimidazo[2,1-f][1,2,4]triazine

Imidazo[2,1-f][1,2,4]triazin-4(3H)-one (2.4 g, 17.63 mmol) was massedinto a 100 mL round-bottom flask under argon atmosphere followed by theinjection of POCl₃ (20 mL) at room temperature. The mixture was heatedto reflux and stirred for 16 h. The volatile was removed under reducepressure. The residue was partitioned between EtOAc (100 mL) and water(30 mL). The organic layer was washed with cold aq NaHCO₃ (saturated,3×20 mL) and brine (20 mL) successively, dried over anhydrous Na₂SO₄,filtered and the filtrate was concentrated under reduced pressure. Theresidue was purified by silica gel column chromatography using pet.ether/EtOAc (5/1) to afford 4-chloroimidazo[2,1-f][1,2,4]triazine.LC-MS: (ES, m/z): 155.0 [M+H]⁺. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.81(s, 1H), 8.65 (d, J=1.2 Hz, 1H), 8.08 (d, J=0.8 Hz, 1H).

Step 5. Synthesis of 4-(methylthio)imidazo[2,1-f][1,2,4]triazine

To a stirred solution of 4-chloroimidazo[2,1-f][1,2,4]triazine (20 g,129 mmol) in THF (500 mL) under argon atmosphere was added NaSMe (13.60g, 194 mmol) at room temperature. The resulting mixture was stirred atroom temperature for 72 hours. The reaction mixture was quenched withaqueous NH₄Cl (saturated, 200 mL) and extracted with EtOAc (2×500 mL).The combined organic layers was washed with brine (2×200 mL), dried overanhydrous Na₂SO₄, filtered and the filtrate was concentrated underreduced pressure. The residue was purified by silica gel columnchromatography using pet. ether/EtOAc (1/1) to afford4-(methylthio)imidazo[2,1-f][1,2,4]triazine. LC-MS: (ES, m/z): 167.2[M+H]⁺. ¹H-NMR: (400 MHz, CDCl₃, ppm): δ 8.47 (s, 1H), 7.90 (d, J=0.8Hz, 1H), 7.76 (d, J=0.4 Hz, 1H), 2.73 (s, 3H).

Step 6: Synthesis of(3R,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)-2-(4-(methylthio)imidazo[2,1-f][1,2,4]triazin-7-yl)tetrahydrofuran-2-ol

To a stirred solution of 4-(methylthio)imidazo[2,1-f][1,2,4]triazine (1g, 6.02 mmol) in THF (25 mL) under argon atmosphere was injected LDA THFsolution (4.5 mL, 9.0 mmol, 2 M) at −78° C. in 5 minutes. The resultingmixture was maintained at −78° C. for 30 minutes, and then a solution of(3R,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)dihydrofuran-2(3H)-one(commercial, 3.27 g, 7.82 mmol) in THF (15 mL) was injected and theresulting mixture was stirred between −78° C. to −50° C. for 2 hours.The reaction was quenched with aqueous NH₄Cl (saturated, 20 mL) andextracted with EtOAc (2×50 mL). The combined organic layers was washedwith brine (2×20 mL), dried over anhydrous Na₂SO₄, filtered and thefiltrate was concentrated under reduced pressure. The residue waspurified by silica gel column chromatography using pet. ether/EtOAc(5/1) to give (3R,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)-2-(4-(methylthio)imidazo[2,1-f][1,2,4]triazin-7-yl)tetrahydrofuran-2-ol.LC-MS: (ES, m/z): 585.1 [M+H]⁺.

Step 7: Synthesis of7-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-4-(methylthio)imidazo[2,1-f][1,2,4]triazine

To a stirred solution of(3R,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)-2-(4-(methylthio)imidazo[2,1-f][1,2,4]triazin-7-yl)tetrahydrofuran-2-ol(1.7 g, 2.91 mmol) in DCM (30 mL) under argon atmosphere were injectedboron trifluoride-diethyl etherate (825.3 mg, 5.82 mmol) andtriethylsilane (1.35 g, 11.63 mmol) at 0° C. successively. The resultingmixture was stirred at 0° C. for additional 16 hours. The reaction wasquenched with aqueous NaHCO₃ (saturated, 20 mL) and extracted with DCM(2×30 mL). The combined organic layers was washed with brine (30 mL),dried over anhydrous Na₂SO₄, filtered and the filtrate was concentratedunder reduced pressure. The residue was purified by silica gel columnchromatography using pet. ether/EtOAc (10/1) to give7-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-4-(methylthio)imidazo[2,1-f][1,2,4]triazine. LC-MS: (ES, m/z): 570.0 [M+H]⁺. ¹H-NMR: (300 MHz,CDCl₃, ppm): δ 8.38 (s, 1H), 7.66 (s, 1H), 7.37-7.26 (m, 15H), 5.56 (d,J=5.4 Hz, 1H), 4.70-4.49 (m, 6H), 4.39 (q, J=4.2 Hz, 1H), 4.34 (t, J=5.4Hz, 1H), 4.15 (t, J=5.1 Hz, 1H), 3.70 (dd, J=3.6 Hz, J=10.5 Hz, 1H),3.60 (dd, J=3.9 Hz, J=10.8 Hz, 1H), 2.70 (s, 3H).

Step 8: Synthesis of7-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)imidazo[2,1-f][1,2,4]triazin-4-amine

To a 80 mL steel bomb, was massed7-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-4-(methylthio)imidazo[2,1-f][1,2,4]triazine (1.4 g, 2.462 mmol). The medium was cooled to −60°C. To this was added isopropanolic ammonia (isopropanol/liquidammonia=2/3, mixed at −60° C., 50 mL). The resulting mixture was heatedto 90° C. and stirred for 16 hours. The reaction mixture was cooled toroom temperature and then concentrated under reduced pressure. Theresidue was purified by silica gel column chromatography using pet.ether/EtOAc (1/1) to give7-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)imidazo[2,1-f][1,2,4]triazin-4-amine. LC-MS: (ES, m/z): 538.3 [M+H]⁺. ¹H-NMR: (400MHz, d₆-DMSO, ppm): δ 8.24 (br s, 1H), 8.15 (br s, 1H), 8.05 (s, 1H),7.49 (s, 1H), 7.36-7.28 (m, 15H), 5.35 (d, J=5.2 Hz, 1H), 4.63 (s, 2H),4.56 (d, J=4.8 Hz, 2H), 4.52 (d, J=2.0 Hz, 2H), 4.45 (t, J=5.2 Hz, 1H),4.22-4.16 (m, 2H), 3.65 (dd, J=3.2 Hz, J=10.8 Hz, 1H), 3.58 (dd, J=4.4Hz, J=10.8 Hz, 1H).

Step 9: Synthesis of(2S,3R,4S,5R)-2-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-5-(hydroxymethyl)tetrahydrofuran-3,4-diol

To a stirred solution of7-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)imidazo[2,1-f][1,2,4]triazin-4-amine(1.2 g, 2.232 mmol) in AcOH (10 mL) was added 20% Pd(OH)₂/C (1.2 g). Themedium was charged with hydrogen (2 atm) and stirred at 25° C. for 24hours. The solid was filtered out and washed with AcOH (2×15 mL). Thecombined filtrate was concentrated under reduced pressure. The residuewas purified by silica gel column chromatography using DCM/MeOH (8/1) toafford (2S,3R,4S,5R)-2-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-5-(hydroxymethyl)tetrahydrofuran-3,4-diol.LC-MS: (ES, m/z): 290.0 [M+Na]⁺. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.22(br s, 1H), 8.15 (br s, 1H), 8.07 (s, 1H), 7.64 (s, 1H), 5.13-5.09 (m,2H), 5.03 (d, J=6.4 Hz, 1H), 4.78 (br s, 1H), 4.32 (t, J=6.0 Hz, 1H),3.99 (t, J=4.8 Hz, 1H), 3.81 (q, J=4.4 Hz, 1H), 3.56 (dd, J=3.2 Hz,J=11.2 Hz, 1H), 3.46 (dd, J=3.6 Hz, J=11.2 Hz, 1H).

Step 10: Synthesis of(6aR,8S,9S,9aS)-8-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-ol

To a stirred solution of (2S,3R,4S,5R)-2-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-5-(hydroxymethyl)tetrahydrofuran-3,4-diol (3.2g, 11.97 mmol) and 1H-imidazole (3.26 g, 47.9 mmol) in DMF (65 mL) underargon atmosphere was injected1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane (3.97 g, 12.57 mmol) at 0°C. The resulting mixture was warmed to 30° C. and stirred for 5 hours.The reaction was quenched with water (70 mL) and extracted with EtOAc(3×100 mL). The combined organic layer was washed with brine (3×100 mL),dried over anhydrous Na₂SO₄, filtered and the filtrate was concentratedunder reduced pressure. The residue was purified by silica gel columnchromatography using pet. ether/EtOAc (3/1) to give(6aR,8S,9S,9aS)-8-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-ol.LC-MS: (ES, m/z): 510.4 [M+H]⁺. ¹H-NMR: (400 MHz, CDCl₃, ppm): δ 8.12(s, 1H), 7.62 (s, 1H), 7.03 (br s, 1H), 6.39 (br s, 1H), 5.31 (d, J=3.2Hz, 1H), 4.68 (dd, J=6.0 Hz, J=7.0 Hz, 1H), 4.47 (q, J=2.8 Hz, 1H),4.10-4.05 (m, 3H), 3.20 (br s, 1H), 1.15-1.05 (m, 28H).

Step 11: Synthesis ofO-((6aR,8S,9S,9aR)-8-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-yl)O-phenylcarbonothioate

To a stirred solution of (6aR,8S,9S,9aS)-8-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-ol(4.0 g, 7.85 mmol) and DMAP (3.83 g, 31.4 mmol) in DCM (160 mL) underargon atmosphere was injected O-phenyl carbonochloridothioate (2.71 g,15.69 mmol) at 0° C. The resulting mixture was stirred at 0° C. foradditional 3 hours. The reaction mixture was concentrated under reducedpressure. The residue was purified by silica gel column chromatographyusing pet. ether/EtOAc (1/3) to giveO-((6aR,8S,9S,9aR)-8-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-yl)O-phenylcarbonothioate. LC-MS: (ES, m/z): δ46.3 [M+H]⁺. ¹H-NMR: (400 MHz,d₆-DMSO, ppm): δ 8.37 (br s, 1H), 8.28 (br s, 1H), 8.02 (s, 1H), 7.67(s, 1H), 7.49 (t, J=8.0 Hz, 2H), 7.34 (t, J=7.4 Hz, 1H), 7.15 (d, J=8.4Hz, 2H), 6.22 (dd, J=2.0 Hz, J=5.2 Hz, 1H), 5.49 (d, J=2.0 Hz, 1H), 4.95(dd, J=5.2 Hz, J=8.8 Hz, 1H), 4.07-3.96 (m, 2H), 3.91-3.88 (m, 1H),1.07-1.04 (m, 28H).

Step 12: Synthesis of7-((6aR,8R,9aS)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-8-yl)imidazo[2,1-f][1,2,4]triazin-4-amine

To a stirred solution ofO-((6aR,8S,9S,9aR)-8-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-yl)O-phenylcarbonothioate (350 mg, 0.542 mmol) and AIBN (133 mg, 0.813 mmol) indegassed toluene (10 mL) under argon atmosphere was injectedtri-n-butyltin hydride (314 mg, 1.084 mmol) at room temperature. Themixture was heated to 80° C. and stirred for 3 hours. The reactionmixture was concentrated under reduced pressure. The residue waspurified by silica gel column chromatography using pet. ether/EtOAc(1/3) to give7-((6aR,8R,9aS)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-8-yl)imidazo[2,1-f][1,2,4]triazin-4-amine.LC-MS: (ES, m/z): 494.5 [M+H]⁺. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.23(br s, 1H), 8.16 (br s, 1H), 8.05 (s, 1H), 7.56 (s, 1H), 5.42 (t, J=7.0Hz, 1H), 4.63 (dd, J=5.8 Hz, J=13.0 Hz, 1H), 3.95 (dd, J=3.2 Hz, J=11.6Hz, 1H), 3.83 (dd, J=6.8 Hz, J=12.0 Hz, 1H), 3.78-3.75 (m, 1H),2.55-2.51 (m, 1H), 2.37-2.32 (m, 1H), 1.07-1.01 (m, 28H).

Step 13: Synthesis of(2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

To a stirred solution of7-((6aR,8R,9aS)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-8-yl)imidazo[2,1-f][1,2,4]triazin-4-amine (2.7 g, 5.47 mmol) in THF (60 mL) wasinjected hydrogen fluoride-pyridine (5.42 g, 54.7 mmol) at 0° C. Themixture was warmed to ambient temperature and stirred for 20 hours. Thereaction mixture was cooled to 0° C., neutralized with solid NaHCO₃ andthen diluted with MeOH (50 mL). The solid was filtered out and thefiltrate was concentrated under reduced pressure. The residue wastreated with DCM/MeOH (20 mL, 100/1, v/v) and stirred for 30 minutes.The white precipitate was collected and dried under vacuum overnight togive(2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol.¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.20 (br s, 1H), 8.13 (br s, 1H),8.06 (s, 1H), 7.60 (s, 1H), 5.42 (dd, J=5.8 Hz, J=10.2 Hz, 1H), 5.12 (d,J=4.0 Hz, 1H), 4.74 (t, J=5.6 Hz, 1H), 4.28-4.25 (m, 1H), 3.81-3.78 (m,1H), 3.42 (t, J=5.4 Hz, 2H), 2.33-2.26 (m, 1H), 2.13-2.09 (m, 1H).

Step 14: Synthesis of7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)imidazo[2,1-f][1,2,4]triazin-4-amine

(2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(200 mg, 0.796 mmol) and 1H-imidazole (217 mg, 3.18 mmol) were massedinto a 10 mL flask under argon atmosphere. To the mixture was injectedanhydrous DMF (2.5 mL), followed by the addition oftert-butylchlorodimethylsilane (360 mg, 2.388 mmol) at 0° C. The mixturewas stirred at 25° C. for 3 h. The resulting mixture was diluted withEtOAc (50 mL), washed with aqueous NaHCO₃ (saturated, 2×15 mL) and brine(20 mL) respectively. The organic layer was collected and dried overanhydrous Na₂SO₄, filtered and concentrated under reduced pressure.

The residue was purified by silica gel column chromatography using pet.ether/EtOAc (35%-52% EtOAc in pet. ether) to give7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)imidazo[2,1-f][1,2,4]triazin-4-amine.LC-MS: (ES, m/z): 480.1 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.20(br s, 1H), 8.13 (br s, 1H), 8.06 (s, 1H), 7.57 (s, 1H), 5.43 (dd, J=5.6Hz, J=10.0 Hz, 1H), 4.46-4.44 (m, 1H), 3.81 (t, J=4.5 Hz, 1H), 3.63-3.51(m, 2H), 2.45-2.36 (m, 1H), 2.16-2.10 (m, 1H), 0.89 (s, 9H), 0.86 (s,9H), 0.10 (s, 6H), 0.02 (d, J=3.6 Hz, 6H).

Step 15: Synthesis of((2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol

7-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)imidazo[2,1-f][1,2,4]triazin-4-amine(350 mg, 0.730 mmol) was massed into a 25 mL round-bottom flask,followed by the injection of THF (4 mL). The medium was cooled to 0° C.To this was added a precooled solution of trifluoroacetic acid/water(1/1, v/v, 2 mL) dropwise with stirring at 0° C. in 10 min. Theresulting mixture was stirred at 0° C. for 2 hours. The reactionprogress was monitored by TLC & LCMS. The resulting solution wasco-evaporated with toluene (3×20 mL) and the residue was re-suspended inaq NaHCO₃ (saturated, 4 mL) and then evaporated to dryness. The residuewas purified by silica gel column chromatography with EtOAc/DCM (1/1) togive((2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol.LC-MS: (ES, m/z): 366.2 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.09(br s, 1H), 8.03 (br s, 1H), 7.96 (s, 1H), 7.51 (s, 1H), 5.31 (q, J=5.4Hz, 1H), 4.70 (t, J=5.7 Hz, 1H), 4.34 (d, J=5.1 Hz, 1H), 3.69 (t, J=4.5Hz, 1H), 3.33-3.28 (m, 2H), 2.34-2.24 (m, 1H), 2.01-1.96 (m, 1H), 0.79(s, 9H), 0.01 (s, 6H).

Step 16: Synthesis of(2S,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde

To a stirred solution of ((2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol(280 mg, 0.766 mmol) in anhydrous acetonitrile (20 mL) under argonatmosphere was added IBX (644 mg, 2.298 mmol) at room temperature. Themixture was heated to 80° C. and stirred for 25 minutes. LCMS indicatedthat the started nucleoside was all consumed. The resulting mixture wascooled to room temperature. The solids were filtered out and thefiltrate was concentrated under reduced pressure to give(2S,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde,which was used for the next reaction step directly without furtherpurification. LC-MS: (ES, m/z): 363.7 [M+H]⁺.

Step 17: Synthesis of((3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol

To a stirred solution of(2S,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde(300 mg, crude) in 1,4-dioxane (4 mL) in a 25 mL round-bottom flask, wasinjected 37% aq formaldehyde (1.0 mL), followed by aq NaOH (1.0 mL, 2.0mmol, 2 N) at 0° C. The resulting mixture was warmed to ambienttemperature and stirred for 16 hours. Upon the started nucleoside wasall consumed, the reaction mixture was neutralized with AcOH (˜0.2 mL).The mixture was diluted with EtOAc (100 mL) and washed successively withwater (2×25 mL), aqueous NaHCO₃ (saturated, 25 mL) and brine (20 mL).The organic layer was dried over anhydrous Na₂SO₄, filtered and thefiltrate was concentrated under reduced pressure give a crude product.The crude product was re-dissolved in EtOH (5 mL) under argon atmosphereand was added sodium borohydride (153 mg, 4.04 mmol) in portions at 0°C. After stirring at ambient temperature for 16 hours, the reactionmixture was neutralized with AcOH (˜0.2 mL) and evaporated to dryness.The residue was partitioned between CHCl₃ (50 mL) and water (25 mL). Theaqueous layer was re-extracted with CHCl₃ (2×25 mL). The combinedorganic layer was washed brine (40 mL), dried over anhydrous Na₂SO₄,filtered and the filtrate was concentrated under reduced pressure. Theresidue was purified by silica gel column chromatography using DCM/MeOH(30/1) to give((3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol.LC-MS: (ES, m/z): 395.8 [M+H]⁺. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.18(br s, 1H), 8.12 (br s, 1H), 8.07 (s, 1H), 7.62 (s, 1H), 5.47 (q, J=5.2Hz, 1H), 4.68 (t, J=5.6 Hz, 1H), 4.53 (d, J=3.6 Hz, 1H), 4.27 (t, J=5.6Hz, 1H), 3.60-3.55 (m, 1H), 3.53-3.51 (m, 2H), 3.34-3.31 (m, 1H),2.56-2.53 (m, 1H), 2.11-2.07 (m, 1H), 0.90 (s, 9H), 0.09 (d, J=2.8 Hz,6H).

Step 18: Synthesis of(2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

To a stirred mixture of((3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol(180 mg, 0.455 mmol) in acetonitrile (20 mL) and DMSO (2 mL) under argonatmosphere was added IBX (382 mg, 1.365 mmol) at room temperature. Theresulting mixture was warmed to 30° C. and stirred for 2 hours. Thesolid was filtered out, washed with CHCl₃ (2×20 mL) and the combinedfiltrate was concentrated under reduced pressure. The residue wasre-dissolved in EtOAc (30 mL), washed successively with aqueous NaHCO₃(saturated, 2×15 mL) and brine (20 mL), dried over anhydrous Na₂SO₄,filtered and the filtrate was concentrated under reduced pressure togive(2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde,which was used for the next reaction step directly without furtherpurification. LC-MS: (ES, m/z): 393.8 [M+H]⁺.

Step 19: Synthesis of((2R,3S,5R)-5-(4-amino-7aH-pyrrolo[3,2-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol

To a stirred mixture of(2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(250 mg, 0.286 mmol, crude) and K₂CO₃ (120 mg, 0.86 mmol) in MeOH (10mL) under argon atmosphere was injected a solution of dimethyl(1-diazo-2-oxopropyl)phosphonate (110 mg, 0.58 mmol) in MeOH (1 mL) at0° C. The resulting mixture was warmed to 30° C. and stirred for 16hours. The reaction mixture was concentrated under reduced pressure. Theresidue was purified by silica gel column chromatography using DCM/MeOH(30/1) to give((2R,3S,5R)-5-(4-amino-7aH-pyrrolo[3,2-d]pyrimidin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol.LC-MS: (ES, m/z): 390.2 [M+H]⁺. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.23(br s, 1H), 8.15 (br s, 1H), 8.08 (s, 1H), 7.67 (s, 1H), 5.54 (t, J=7.8Hz, 1H), 5.16 (t, J=6.2 Hz, 1H), 4.53 (dd, J=4.6 Hz, J=6.2 Hz, 1H), 3.55(dd, J=5.2 Hz, J=11.6 Hz, 1H), 3.45 (dd, J=7.0 Hz, J=11.8 Hz, 1H), 3.42(s, 1H), 2.56-2.53 (m, 1H), 2.23-2.17 (m, 1H), 0.91 (s, 9H), 0.10 (d,J=3.2 Hz, 6H).

Step 20. Synthesis of(2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(22)

To a stirred solution of((2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(150 mg, 0.385 mmol) in anhydrous THF (5 mL) under argon atmosphere wasinjected TBAF THF solution (0.385 mL, 0.385 mmol, 1 M) at 0° C. Themixture was warmed to room temperature and stirred for 16 hours. Thereaction progress was monitored by TLC & LCMS. The resulting mixture wasconcentrated under reduced pressure. The residue was purified by silicagel column chromatography using DCM/MeOH (24/1) to give the titlecompound 22. LC-MS: (ES, m/z): 309.00 [M+H]⁺. ¹H-NMR: (400 MHz, d₆-DMSO,ppm): δ 8.21 (br s, 1H), 8.14 (br s, 1H), 8.07 (s, 1H), 7.64 (s, 1H),5.53 (t, J=7.6 Hz, 1H), 5.34 (d, J=5.2 Hz, 1H), 5.07 (t, J=6.4 Hz, 1H),4.35 (q, J=6.0 Hz, 1H), 3.56 (dd, J=5.6 Hz, J=12.0 Hz, 1H), 3.48 (dd,J=7.0 Hz, J=11.8 Hz, 1H), 3.41 (s, 1H), 2.46-2.41 (m, 1H), 2.28-2.21 (m,1H).

Example 23: Synthesis of(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(23)

Step 1: Synthesis of(3R,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-ol

To a stirred suspension of NaH 60% dispersed in mineral oil (1.878 g,46.9 mmol) in anhydrous DME (dimethylether) (150 mL) under argonatmosphere was injected diethyl (cyanomethyl)phosphonate (11.88 g, 67.1mmol) at 0° C. over 10 minutes. The mixture was warmed to 25° C. andmaintained for 0.5 h and then a solution of(3R,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-ol(14.1 g, 33.5 mmol) in dry DME (100 mL) was added drop-wise withstirring at 0° C. over 30 minutes. The resulting mixture was warmed to25° C. again and maintained for 2 hours. The resulting mixture wasdiluted with H₂O (300 mL) and extracted with Et₂O (3×500 mL). Thecombined organic layers was washed with brine (500 mL), dried overanhydrous Na₂SO₄, filtered and the filtrate was concentrated underreduced pressure. The residue was purified by flash silica gel columnchromatography using EtOAc/pet. ether (5%-20% EtOAc in pet. ether) toafford2-((3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)acetonitrile.LC-MS: (ES, m/z): 444.21 [M+H]⁺. ¹H-NMR: (300 MHz, CDCl₃, ppm): δ7.33-7.31 (m, 15H), 4.63-4.43 (m, 6H), 4.25-4.13 (m, 2H), 3.95 (dd,J=3.0 Hz, J=4.8 Hz, 1H), 3.77 (dd, J=5.4 Hz, J=6.9 Hz, 1H), 3.53-3.45(m, 2H), 2.78-2.75 (m, 0.4 H), 2.66 (dd, J=4.8 Hz, J=16.8 Hz, 0.8 H),2.50 (dd, J=4.8 Hz, J=16.8 Hz, 0.8 H).

Step 2: Synthesis of2-((3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-3-(dimethylamino)acrylonitrile

To a stirred solution of 2-((3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)acetonitrile (12.6 g, 28.4 mmol) in DCM (90mL) under argon atmosphere were injected dry DMF (2.54 mL, 32.8 mmol)followed by 1-tert-butoxy-N,N,N′,N-tetramethylmethanediamine (19.80 g,114 mmol) at 0° C. over 5 minutes. The resulting mixture was warmed to25° C. and stirred for 16 hours. The resulting mixture was concentratedunder reduced pressure. The residue was purified by flash silica gelcolumn chromatography using EtOAc/pet. ether (15%-35% EtOAc in pet.ether) to afford2-((3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-3-(dimethylamino)acrylonitrile.LC-MS: (ES, m/z): 499.25 [M+H]⁺. ¹H-NMR: (300 MHz, CDCl₃, ppm): δ7.33-7.30 (m, 15H), 6.47 (s, 1H), 4.65-4.53 (m, 6H), 4.32 (d, J=7.2 Hz,1H), 4.19-4.15 (m, 1H), 4.00-3.90 (m, 2H), 3.59-3.46 (m, 2H), 3.04 (s,6H).

Step 3. Synthesis of2-((3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-3-hydrazinylacrylonitrile

To a stirred solution of 2-((3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-3-(dimethylamino)acrylonitrile (12.9 g,25.9 mmol) in MeOH (90 mL) were added hydrazine hydrate (21.15 g, 647mmol), H₂O (3.0 mL, 167 mmol) and hydrazine hydrochloride (2.66 g, 38.8mmol) successively at room temperature. The resulting mixture was heatedto 65° C. and stirred for 16 hours. The final mixture was concentratedunder reduced pressure. The residue was diluted with H₂O (500 mL) andextracted with EtOAc (3×500 mL). The combined organic layers was washedwith brine (500 mL), dried over anhydrous Na₂SO₄, filtered and thefiltrate was concentrated under reduced pressure to afford2-((3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-3-hydrazinylacrylonitrile,which was used for the next reaction step directly without furtherpurification. LC-MS: (ES, m/z): 486.23 [M+H]⁺.

Step 4: Synthesis of4-[(2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-[(benzyloxy)methyl]oxolan-2-yl]-1H-pyrazol-5-amine

2-((3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-3-hydrazinylacrylonitrile(18 g, 37.1 mmol) was put into a 1000-mL round-bottom flask followed bythe injection of ACN (200 mL). The mixture was refluxed for 48 hours.The resulting mixture was concentrated under reduced pressure. Theresidue was purified by flash silica gel column chromatography usingMeOH/DCM (2% to 10% MeOH in DCM) to afford4-[(2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-[(benzyloxy)methyl]oxolan-2-yl]-1H-pyrazol-5-amine.LC-MS: (ES, m/z): 486.23 [M+H]⁺. ¹H-NMR: (400 MHz, CDCl₃, ppm): δ7.40-7.24 (m, 16H), 4.97 (d, J=6.8 Hz, 1H), 4.68 (d, J=12.0 Hz, 1H),4.62-4.44 (m, 5H), 4.24-4.22 (m, 1H), 4.10-4.04 (m, 2H), 3.71 (dd, J=3.0Hz, J=10.2 Hz, 1H), 3.63-3.50 (m, 1H).

Step 5. Synthesis of8-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)pyrazolo[1,5-a][1,3,5]triazin-4-amine

To a stirred mixture of cyanamide (50 g, 1189 mmol) was addedtrimethoxymethane (505 g, 4757 mmol) and the mixture was heated to 105°C. and stirred for 5 minutes. To the above was injected formic acid(4.38 g, 95 mmol) at 105° C. over 5 minutes. After the resultingsolution was stirred at 105° C. for 5 hours, the reaction mixture wascooled down to room temperature. The solids were filtered out and thefiltrate was concentrated under reduced pressure. The product wascollected by distillation (0.1 mm Hg, 60° C. to 70° C.) to give(E)-methyl N-cyanoformimidate (50 g, 0.595 mol).

To a stirred solution of (E)-methyl N-cyanoformimidate (21.82 g, 259mmol) in toluene (150 mL) under argon atmosphere was added a solution of4-((3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)-1H-pyrazol-5-amine(21 g, 43.2 mmol) in toluene (30 mL) at room temperature. The resultingmixture was heated to 90° C. and stirred for 20 hours. The resultingsolution was concentrated under reduced pressure. The residue waspurified by flash silica gel column chromatography using EtOAc/pet.ether (30% to 50% EtOAc in pet. ether) to afford8-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)pyrazolo[1,5-a][1,3,5]triazin-4-amine. LC-MS: (ES,m/z): 538.24 [M+H]⁺. ¹H-NMR: (300 MHz, CDCl₃, ppm): δ 8.05 (s, 1H), 7.99(s, 1H), 7.31-7.23 (m, 15H), 6.67 (br s, 2H), 5.33 (d, J=5.4 Hz, 1H),4.67-4.50 (m, 6H), 4.35-4.29 (m, 2H), 4.15-4.11 (m, 1H), 3.72 (dd, J=3.9Hz, J=10.5 Hz, 1H), 3.62 (dd, J=4.2 Hz, J=10.8 Hz, 1H).

Step 6: Synthesis of(2S,3R,4S,5R)-2-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-5-(hydroxymethyl)tetrahydrofuran-3,4-diol

To a stirred mixture of8-((2S,3S,4R,5R)-3,4-bis(benzyloxy)-5-((benzyloxy)methyl)tetrahydrofuran-2-yl)pyrazolo[1,5-a][1,3,5]triazin-4-amine(10 g, 18.60 mmol) in AcOH (250 mL) was added palladium hydroxide 20% oncarbon. The mixture was charged with hydrogen (1.5-2 atm) and stirred at25° C. for 14 hours. The solids were filtered out. The filtrate wasconcentrated under reduced pressure. The residue was triturated with DCM(150 mL) to form a white precipitate. The precipitate was collected byfiltration, washed with DCM and dried in vacuo overnight to give(2S,3R,4S,5R)-2-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-5-(hydroxymethyl)tetrahydrofuran-3,4-diol.LC-MS: (ES, m/z): 268.10 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.76(br s, 1H), 8.41 (br s, 1H), 8.19 (s, 1H), 8.06 (s, 1H), 4.96-4.91 (m,2H), 4.86-4.81 (m, 2H), 4.20 (q, J=6.0 Hz, 1H), 3.98 (q, J=4.5 Hz, 1H),3.78 (q, J=3.9 Hz, 1H), 3.61-3.55 (m, 1H), 3.49-3.43 (m, 1H).

Step 7: Synthesis of(6aR,8S,9S,9aS)-8-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-ol

To a stirred solution of(2S,3R,4S,5R)-2-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-5-(hydroxymethyl)tetrahydrofuran-3,4-diol(2.2 g, 8.23 mmol) and 1H-imidazole (1.681 g, 24.70 mmol) in dry DMF(100 mL) under argon atmosphere was injected1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane (2.86 g, 9.06 mmol) at 0°C. over 4 minutes. The resulting mixture was warmed to 25° C. andstirred for 3 hours. The residue was diluted with H₂O (50 mL) andextracted with EtOAc (3×50 mL). The combined organic layers was washedwith brine (2×50 mL), dried over anhydrous Na₂SO₄, filtered and thefiltrate was concentrated under reduced pressure. The residue waspurified by flash silica gel column chromatography using EtOAc/pet.ether (30%-50% EtOAc in pet. ether) to afford(6aR,8S,9S,9aS)-8-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-ol.LC-MS: (ES, m/z): 510.25 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.72(br s, 1H), 8.42 (br s, 1H), 8.08 (s, 1H), 8.02 (s, 1H), 5.08 (d, J=4.8Hz, 1H), 4.91 (d, J=1.8 Hz, 1H), 4.41 (dd, J=5.4 Hz, J=8.1 Hz, 1H),4.30-4.28 (m, 1H), 3.99-3.86 (m, 3H), 1.04-1.00 (m, 28H).

Step 8: Synthesis of8-((6aR,8R,9aS)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-8-yl)pyrazolo[1,5-a][1,3,5]triazin-4-amine

To a stirred solution of(6aR,8S,9S,9aS)-8-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-9-ol(3.90 g, 7.65 mmol) in dry DCE (120 mL) under argon atmosphere was added1,1′-thiocarbonyldiimidazole (1.704 g, 9.56 mmol) at room temperature.The resulting mixture was heated to 85° C. and stirred for 1.5 hours.TLC indicated the starting nucleoside was all consumed. The resultingsolution was concentrated under reduced pressure to give crudeimidazolyl intermediate which was immediately re-dissolved in degassedtoluene (120 mL) under argon atmosphere. To the above was added AIBN(1.88 g, 11.48 mmol) followed by the injection of tributylstannane (4.45g, 15.30 mmol) at 25° C. over 2 minutes. The resulting mixture washeated to 80° C. and stirred for 3 hours. The resulting solution wasconcentrated under reduced pressure. The crude residue was purified byflash silica gel column chromatography using EtOAc/pet. ether (30%-50%EtOAc in pet. ether) to afford8-((6aR,8R,9aS)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-8-yl)pyrazolo[1,5-a][1,3,5]triazin-4-amine.LC-MS: (ES, m/z): 494.25 [M+H]⁺. ¹H-NMR: (300 MHz, CDCl₃, ppm): δ 8.18(s, 1H), 8.06 (s, 1H), 6.61 (br s, 2H), 5.40 (t, J=7.5 Hz, 1H),4.70-4.65 (m, 1H), 4.10 (dd, J=3.0 Hz, J=10.8 Hz, 1H), 3.95-3.81 (m,2H), 2.52-2.38 (m, 2H), 1.08-1.05 (m, 28H).

Step 9: Synthesis of(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol

To a stirred solution of 8-((6aR,8R,9aS)-2,2,4,4-tetraisopropyltetrahydro-6H-furo[3,2-f][1,3,5,2,4]trioxadisilocin-8-yl)pyrazolo[1,5-a][1,3,5]triazin-4-amine(1.5 g, 3.04 mmol) in anhydrous THF (35 mL) under argon atmosphere wasinjected HF-Pyridine solution (1.5 mL, 11.65 mmol) at 0° C. over 5minutes. The mixture was warmed to 25° C. and stirred for 4 hours.

The resulting mixture was neutralized by the addition of solid NaHCO₃and then diluted with MeOH (30 mL). The un-dissolved solid was filteredout. The filtrate was concentrated under reduced pressure and thentriturated with EtOAc (20 mL). A white precipitate was formed andcollected by filtration then dried in vacuo overnight to afford(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol.LC-MS: (ES, m/z): 252.10 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.71(br s, 1H), 8.39 (br s, 1H), 8.19 (s, 1H), 8.05 (s, 1H), 5.25 (q, J=5.4Hz, 1H), 5.03 (d, J=3.9 Hz, 1H), 4.87 (t, J=6.0 Hz, 1H), 4.26-4.24 (m,1H), 3.76-3.74 (m, 1H), 3.52-3.40 (m, 2H), 2.32-2.22 (m, 1H), 2.04-1.98(m, 1H)

Step 10: Synthesis of8-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)pyrazolo[1,5-a][1,3,5]triazin-4-amine

To a stirred solution of(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-(hydroxymethyl)tetrahydrofuran-3-ol(540 mg, 2.149 mmol) and 1H-imidazole (512 mg, 7.52 mmol) in DMF (10 mL)under argon atmosphere was added TBS-Cl (972 mg, 6.45 mmol) at 0° C.over 1 minutes. The resulting mixture was warmed to 25° C. and stirredfor 2 hours. The resulting solution was diluted with H₂O (50 mL) andextracted with EtOAc (3×50 mL). The combined organic layers was washedwith brine (2×50 mL), dried over anhydrous Na₂SO₄, filtered and thefiltrate was concentrated under reduced pressure. The residue waspurified by flash silica gel column chromatography using EtOAc/pet.ether (20% EtOAc in pet. ether) to afford8-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)pyrazolo[1,5-a][1,3,5]triazin-4-amine.LC-MS: (ES, m/z): 480.27 [M+H]⁺. ¹H-NMR: (400 MHz, CDCl₃, ppm): δ 8.18(s, 1H), 8.10 (s, 1H), 6.80 (br s, 2H), 5.49 (q, J=5.2 Hz, 1H), 4.51 (d,J=5.2 Hz, 1H), 3.98 (t, J=4.0 Hz, 1H), 3.74 (dd, J=3.8 Hz, J=10.6 Hz,1H), 3.63 (dd, J=6.4 Hz, J=10.8 Hz, 1H), 2.39-2.32 (m, 1H), 2.22-2.17(m, 1H), 0.93-0.92 (m, 18H), 0.11-0.05 (m, 12H).

Step 11: Synthesis of((2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol

To a stirred solution of8-((2R,4S,5R)-4-((tert-butyldimethylsilyl)oxy)-5-(((tert-butyldimethylsilyl)oxy)methyl)tetrahydrofuran-2-yl)pyrazolo[1,5-a][1,3,5]triazin-4-amine(800 mg, 1.667 mmol) in THF (16 mL) was injected a pre-cooled solutionof TFA/H₂O (8 mL, v/v, 1/1) at 0° C. over 5 minutes. The resultingmixture was stirred at 0° C. for 1.5 hours. The reaction progress wasmonitored by TLC. The resulting solution was co-evaporated with toluene(3×50 mL) below 25° C. and the residue was re-dissolved in MeOH/DCM (20mL, v/v, 1/2) and the mixture was neutralized with solid NaHCO₃. Thesolid was filtered out and the filtrate was concentrated under reducedpressure. The crude product was purified by flash silica gel columnchromatography using MeOH/DCM (2% to 10% MeOH in DCM) to afford((2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol.LC-MS: (ES, m/z): 366.19 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.70(br s, 1H), 8.38 (br s, 1H), 8.19 (s, 1H), 8.05 (s, 1H), 5.24 (q, J=5.4Hz, 1H), 4.92 (t, J=6.0 Hz, 1H), 4.42 (d, J=4.8 Hz, 1H), 3.75 (dd, J=3.6Hz, J=4.8 Hz, 1H), 3.46-3.43 (m, 2H), 2.39-2.30 (m, 1H), 2.00-1.94 (m,1H), 0.90 (s, 9H), 0.11 (s, 6H).

Step 12: Synthesis of(2S,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde

To a stirred suspension of((2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-yl)methanol(350 mg, 0.958 mmol) in anhydrous ACN (40 mL) under argon atmosphere wasadded IBX (804 mg, 2.87 mmol) at 25° C. The resulting mixture was heatedto 80° C. and stirred for 1 hour. The solid was filtered out. Thefiltrate was concentrated under reducing pressure to afford(2S,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde,which was used for the next reaction step directly without furtherpurification. LC-MS: (ES, m/z): 364.17 [M+H]⁺.

Step 13: Synthesis of((3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol

To a stirred solution of(2S,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2-carbaldehyde(349 mg, 0.960 mmol) in 1,4-dioxane (25 mL) in a 100 mL round-bottomflask, was injected formaldehyde 37% aqueous solution (5 mL), followedby the injection of NaOH aqueous solution (5 mL, 2 N) at roomtemperature over 5 minutes. The resulting mixture was stirred at roomtemperature for 5 hours. Upon the started nucleoside was all consumed,the reaction mixture was neutralized with AcOH (˜0.5 mL). The mixturewas diluted with EtOAc (50 mL) and washed successively with H₂O (2×20mL), aq NaHCO₃ (saturated, 2×20 mL) and brine (20 mL). The organic layerwas dried over Na₂SO₄, filtered and the filtrate was concentrated underreduced pressure. The residue was re-dissolved in anhydrous EtOH (40 mL)and added sodium tetrahydroborate (72.6 mg, 1.920 mmol) in portions at0° C. under argon atmosphere. After stirring at 25° C. for 16 hours, thereaction mixture was neutralized with AcOH (0.2 mL) and concentratedunder reduced pressure. The residue was partitioned between CHCl₃ (30mL) and H₂O (15 mL). The aqueous layer was re-extracted with CHCl₃ (2×15mL). The combined organic layer was washed with brine (20 mL), driedover Na₂SO₄, filtered and the filtrate was concentrated under reducedpressure. The residue was purified by flash silica gel columnchromatography using MeOH/DCM (3.5% MeOH in DCM) to give((3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol.LC-MS: (ES, m/z): 396.20 [M+H]⁺. ¹H-NMR: (300 MHz, d₆-DMSO, ppm): δ 8.70(br s, 1H), 8.38 (br s, 1H), 8.20 (s, 1H), 8.05 (s, 1H), 5.30 (dd, J=5.1Hz, J=11.1 Hz, 1H), 4.84 (t, J=6.0 Hz, 1H), 4.50 (d, J=4.2 Hz, 1H), 4.22(dd, J=5.1 Hz, J=6.3 Hz, 1H), 3.62-3.48 (m, 3H), 3.41-3.31 (m, 1H),2.57-2.50 (m, 1H), 1.95 (dd, J=5.1 Hz, J=12.6 Hz, 1H), 0.90 (s, 9H),0.11 (s, 6H).

Step 14: Synthesis of(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde

To a stirred suspension of((3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)tetrahydrofuran-2,2-diyl)dimethanol(190 mg, 0.480 mmol) in ACN/DMSO (8 mL, v/v, 10/1) under argonatmosphere was added IBX (404 mg, 1.441 mmol) at 25° C. The resultingmixture was stirred at 30° C. for 7 hours. The solid was filtered out.The filtrate was concentrated under reduced pressure to give(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehydewhich was used for the next reaction step directly without furtherpurification. LC-MS: (ES, m/z): 394.18 [M+H]⁺.

Step 15: Synthesis of((2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol

To a stirred solution of(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)-2-(hydroxymethyl)tetrahydrofuran-2-carbaldehyde(189 mg, 0.480 mmol) in dry MeOH (6 mL) under argon atmosphere was addedK₂CO₃ (199 mg, 1.441 mmol) followed by the injection of a solution ofdimethyl (1-diazo-2-oxopropyl)phosphonate (185 mg, 0.961 mmol) in MeOH(1.5 mL) at 0° C. over 3 minutes. The reaction mixture was warmed slowlyto 25° C. and then stirred at 25° C. for 16 hours. The resulted mixturewas concentrated under reduced pressure. The residue was purified byflash silica gel column chromatography using MeOH/DCM (2% to 10% MeOH inDCM) to afford((2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol.LC-MS: (ES, m/z): 390.19 [M+H]⁺. ¹H-NMR: (300 MHz, CDCl₃, ppm): δ 8.17(s, 1H), 7.98 (s, 1H), 6.43 (br s, 2H), 5.54 (dd, J=5.7 Hz, J=10.5 Hz,1H), 4.61 (d, J=4.2 Hz, 1H), 3.97 (d, J=12.3 Hz, 1H), 3.76 (d, J=12.0Hz, 1H), 2.70-2.61 (m, 1H), 2.54 (s, 1H), 2.20-2.14 (m, 1H), 0.95 (s,9H), 0.12 (d, J=6.0 Hz, 6H).

Step 16:(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(23)

To a stirred solution of((2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-3-((tert-butyldimethylsilyl)oxy)-2-ethynyltetrahydrofuran-2-yl)methanol(120 mg, 0.308 mmol) in THF (5 mL) under argon atmosphere was injectedTBAF THF solution (0.462 mL, 0.462 mmol, 1.0 M) at 0° C. over 2 minutes.The mixture was stirred at 20° C. for 26 hours. The resulting mixturewas concentrated under reduced pressure. The residue was purified byflash silica gel column chromatography using MeOH/DCM (5% to 10% MeOH inDCM) to give crude product. The crude product (90 mg) was furtherpurified by Prep-HPLC with the following conditions (1#-Pre-HPLC-011(Waters)): Column, X-bridge C18 19×150 mm; mobile phase, water withNH₄HCO₃ (10 mmol/L) and ACN (4% ACN up to 9% in 6 min, hold 95% for 2minutes, down to 5% in 2 minutes); Detector, UV 254 & 220 nm. Theproduct-containing fractions were collected and lyophilized overnight togive(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol.LC-MS: (ES, m/z): 276.10 [M+H]⁺. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.71(br s, 1H), 8.43 (br s, 1H), 8.20 (s, 1H), 8.05 (s, 1H), 5.36 (t, J=7.6Hz, 1H), 5.26-5.22 (m, 2H), 4.34 (dd, J=4.8 Hz, J=11.2 Hz, 1H), 3.58(dd, J=5.2 Hz, J=11.6 Hz, 1H), 3.49 (dd, J=7.6 Hz, J=11.6 Hz, 1H), 3.37(s, 1H), 2.44-2.37 (m, 1H), 2.16-2.12 (m, 1H).

RT Polymerase Assay

Full-length wild-type and 2 mutant RT proteins were expressed inEscherichia coli BL21(DE3) cells and purified. Briefly, theheterodimeric nucleic acid substrate used in the HIV-1 RT polymerasereactions was generated by annealing biotinylated DNA primer to a 500nucleotide RNA template. The HIV-1 RT enzyme (final concentration of 50μM) was combined with an inhibitor compound or DMSO (10% DMSO in thefinal reaction mixture) in assay buffer (62.5 mM Tris-HCl, pH 7.8, 1.25mM dithiothreitol, 7.5 mM MgCl2, 100 mM KCl, 0.03% CHAPS, 0.125 mMEGTA). This mixture was pre-incubated for 30 minutes at room temperaturein microtiter plates. The polymerization reaction was initiated by theaddition of template/primer substrate (final concentration: 16.6 nM) anddNTPs (final concentration: 2 μM dCTP, dGTP, dATP, and 66.6 nM Ru-dUTP).After 90 min of incubation at 37° C., reactions were quenched by theaddition of EDTA (25 mM). The resulting mixture was incubated for anadditional 5 minutes at room temperature followed by transferring thesolution (50 μL) to blocked avidin plate from Meso Scale Discovery(MSD). The mixtures were incubated at room temperature for 60 min priorto the quantification of the reaction product via an ECL 6000 imagerinstrument. The resulting data is shown in Table 2.

TABLE 2 Example No. Structure dNTP IC₅₀ (nM) 13

933 14

210 15

6237 16

1820 17

842 18

4150 19

3542 20

1292 21

905

Viking Assay/CTG Viking Assay:

Assessing Antiviral Potency in a Multiple Round HIV-1 Infection Assay.

HIV-1 replication was monitored using MT4-gag-GFP clone D3 (hereafterdesignate MT4-GFP), which are MT-4 cells modified to harbor a GFPreporter gene, the expression of which is dependent on the HIV-1expressed proteins tat and rev. Productive infection of an MT4-GFP cellwith HIV-1 results in GFP expression approximately 24 h post-infection.

MT4-GFP cells were maintained at 37° C./5% CO₂/90% relative humidity inRPMI 1640 supplemented with 10% fetal bovine serum, 100 U/mLpenicillin/streptomycin, and 400 μg/mL G418 to maintain the reportergene. For infections, MT4-GFP cells were placed in the same mediumlacking G418 and infected overnight with H9IIIB virus at an approximatemultiplicity of infection of 0.01 in the same incubation conditions.Cells were then washed and re-suspended in either RPMI 1640 containing10% or 50% normal human serum at 1.6×10⁵ cells/mL (10% or 50% NHSconditions) or in 100% normal human serum at 2×10⁵ cells/mL (100% NHSconditions). Compound plates were prepared by dispensing compoundsdissolved in DMSO into wells of 384 well poly D lysine-coated plates(0.2 μl/well) using an ECHO acoustic dispenser. Each compound was testedin a 10 point serial 3-fold dilution (typical final concentrations: 8.4μM-0.43 nM). Controls included no inhibitor (DMSO only) and acombination of three antiviral agents (efavirenz, indinavir, and anintegrase strand transfer inhibitor at final concentrations of 4 μMeach). Cells were added (50 μL/well) to compound plates and the infectedcells were maintained at 37° C./5% CO₂/90% relative humidity.

Infected cells were quantified at two time points, ˜48 h and ˜72 hpost-infection, by counting the number of green cells in each well usingan Acumen eX3 scanner. The increase in the number of green cells over˜24 h period gives the reproductive ratio, R₀, which is typically 5-15and has been shown experimentally to be in logarithmic phase (data notshown). Inhibition of R₀ is calculated for each well, and IC₅₀sdetermined by non-linear 4-parameter curve fitting.

CTG Assay: Assessing Cytotoxicity in CellTiter-Glo Luminescent CellViability Assay (CTG).

MT4-GFP cells were seeded in RPMI 1640 supplemented with 10% fetalbovine serum, 100 U/mL penicillin/streptomycin overnight at 37° C./5%CO₂/90% relative humidity. Cells were then washed and resuspended inRPMI 1640 containing 10% normal human serum at a density of 0.8×10⁵cells/mL. Compound plates were prepared by dispensing compoundsdissolved in DMSO into wells of 384 well solid black plates (Corning3571) using an ECHO acoustic dispenser (0.2 μl/well). Each compound wastested in a 10 point serial 3-fold dilution (final concentrations: 8.4μM-0.43 nM). Controls included DMSO. Cells were added (50 μL/well) tocompound plates and were maintained at 37° C./5% CO₂/90% relativehumidity. CTG reagent (Promega, G7573) was added to the cell platesafter 48 h incubation according to the manufacturer's description.Luminescence signals were recorded on EnVision plate reader(PerkinElmer). LD₅₀s were determined by non-linear 4-parameter curvefitting. The resulting data is shown in Table 3 with the marketed HIVnucleoside reverse transcriptase inhibitor AZT (azidothymidine,zidovudine) included as a control.

TABLE 3 Viking, IC₅₀ Structure (10% NHS)(nM) CTG (μM) AZT

37 >8.4 Example Viking, IC₅₀ No. Structure (10% NHS)(nM) CTG (μM) 1

1.3 >8.4 2

1.6 >8.4 3

485 >8.4 4

4.0 >8.4 5

209 >8.4 6

128 >8.4 7

1030 >8.4 8

194 >8.4 9

10.2 >8.4 10

128 >8.4 11

17.2 >8.4 12

735 >8.4 22

38 >8.4 23

64 >8.4

Antiviral Persistence

HIV-1 replication was monitored using MT4-gag-GFP clone D3 (hereafterdesignate MT4-GFP), which are MT-4 cells modified to harbor a GFPreporter gene, the expression of which is dependent on the HIV-1expressed proteins tat and rev. Productive infection of an MT4-GFP cellwith HIV-1 results in GFP expression approximately 24 h post-infection.MT4-GFP cells were maintained at 37° C./5% CO₂/90% relative humidity inRPMI 1640 supplemented with 10% fetal bovine serum, 100 U/mLpenicillin/streptomycin, and 400 μg/mL G418 to maintain the reportergene. For 72 hour time point persistence assay (72 h plate) and 24 hourtime point control assay (24 h plate), MT4-GFP cells were washed andre-suspended in RPMI 1640 containing 10% normal human serum at either1.6×10⁵ or 2.4×10⁵ cells/mL (10% NHS). Compound plates were prepared bydispensing compounds dissolved in DMSO into wells of 384 well cellculture plates (0.205 l/well) using an ECHO acoustic dispenser. Eachcompound was tested in a 10 point serial 3-fold dilution (typical finalconcentrations: 4.2 μM-0.21 nM). Controls included no inhibitor (DMSOonly) and a combination of three antiviral agents (efavirenz, indinavir,and an integrase strand transfer inhibitor at final concentrations of 4μM each). Cells were added (50 μL/well) to compound plates and wereincubated at 37° C./5% CO₂/90% relative humidity for 24 hours. The cellswere washed with 5×40 uL of RPMI 1640 supplemented with 10% NHS and 100U/mL penicillin/streptomycin. 72 h plate was return back to 37° C.incubator for additional 48 hour incubation. 40 uL of the cells fromeach well of the 24 h plate or the 72 h plate (after 48 hour incubationpost wash) were transferred to a poly-D-lysine coated plate. The cellswere then infected with H9IIIB virus at an approximate multiplicity ofinfection of 0.1 in the same incubation conditions.

Infected cells were quantified at ˜24 h post-infection, by counting thenumber of green cells in each well using an Acumen eX3 scanner. IC₅₀sfor the compounds in Table 4 were determined by non-linear 4-parametercurve fitting.

The antiviral persistence assay is meant to assess for the persistenceof antiviral activity upon removal of the nucleoside. The data in Table4 demonstrates the antiviral persistence of compounds of this inventionin comparison to the marketed nucleoside AZT. The publication AIDSResearch and Therapy, 2009, 6:5, highlights the value of antiviralpersistence.

TABLE 4 IC₅₀ 24 h IC₅₀ 72 h Fold shift IC₅₀ Structure (nM) (nM) 72 h/24h AZT

37 4713 127 EXAMPLE IC₅₀ 24 h IC₅₀ 72 h Fold shift IC₅₀ No. Structure(nM) (nM) 72 h/24 h 1

0.8 36 45 2

6.6 193 29 3

470 2500 5.3 4

9.6 360 37.5 5

22000 >42000 >1.9 6

99 970 9.8 7

17000 17000 1 8

840 29000 34.5 9

37 270 7.3 10

170 1800 10.5 11

12.4 1950 157 12

880 25000 28 22

38 350 9.2 23

64 700 10.9

Adenosine Deaminase (ADA) Half-Life

The data in Table 5 was generated by reacting a substrate compound withhuman ADA type 1 in the presence of Tris-HCl buffer (pH 7.5) at 40° C.and monitoring by LCMS for consumption of starting material. The timenecessary for 50% conversion to the corresponding inosine product isnoted as the T_(1/2) in Table 5. It is known that deamination byadenosine deaminase decreases the therapeutic potential ofadenosine-like nucleoside inhibitors especially in vivo (see referencesbelow). The compounds shown in Table 5 have been shown to have varyingdegrees of stability to adenosine deaminase when compared to EDA((2R,3S,5R)-5-(6-amino-9H-purin-9-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol)and natural deoxyadenosine. It is possible that compounds that are moreresistant to ADA will have better pharmacokinetic properties.

REFERENCES

Journal of Medicinal Chemistry 1996, 39, 19, 3847; ChemicalPharmaceutical Bulletin. 1994, 42, 8, 1688-1690; Antimicrobial Agentsand Chemotherapy (2013), 57(12), 6254-6264; Collection of CzechoslovakChemical Communications (2006), 71(6), 769-787 Microbiologica (1995),18(4), 359-70; J Antivir Antiretrovir S10. doi: 10.4172/jaa.S10-002.

Conversion of Compound 2 to Inosine Product 2A7-((2R,4S,5R)-5-ethynyl-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-yl)-5-fluoro-3H-pyrrolo[2,3-d]pyrimidin-4(7H)-one (2A)

Tris-HCl buffer (pH 7.5, 5 mL) was injected into a 25-mL round-bottomflask. The mixture was heated to reflux for 30 minutes. Then the mixturewas cooled to 30° C. and(2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol(Example compound 2, 7 mg, 0.024 mmol) was added, followed by theaddition of adenosine deaminase (3 mg, ˜33 units). The resulting mixturewas stirred at 40° C. and stirred for 4 days. The reaction mixture wasconcentrated under vacuum and the residue was purified bypreparative-HPLC with the following conditions: Column: X-Bridge C18,19*150 mm, 5 um; mobile phase, water with 10 mmol ammonium bicarbonateand acetonitrile (6% acetonitrile up to 30% in 5 min, hold 95% for 2min, down to 40% in 2 min); Detector, uv 254&220 nm. Theproduct-containing fractions were collected and lyophilized to give thetitle compound 2A as a solid. ¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 11.58(brs, 1H), 7.86 (s, 1H), 7.22 (d, J=1.6 Hz, 1H), 6.44 (t, J=5.8 Hz, 1H),5.47 (d, J=4.8 Hz, 1H), 5.26-5.22 (m, 1H), 4.39-4.35 (m, 1H), 3.55-3.45(m, 2H), 3.42 (s, 1H), 2.41-2.24 (m, 2H). ¹⁹F-NMR: (376 MHz, d₆-DMSO,ppm): δ −165.50 (s, 1F). LC-MS: (ES, m/z): 294.15 [M+H]⁺.

The general procedures described above for conversion of compound 2 to2A were applied to each of the substrate compounds in Table 5, andresulted in production of the inosine products shown for Deoxy-adenosineand EDA, as well as inosine products 1A, 2A, 11A, 22A, and 23A.

Using the described procedures, conversion of compounds 4, 8 and 9 to4A, 8A and 9A, respectively, was not detected (NA=substrate insensitiveto adenosine deaminase).

Compound 1A:7-((2R,4S,5R)-5-ethynyl-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-yl)-3H-pyrrolo[2,3-d]pyrimidin-4(7H)-one

¹H-NMR: (400 MHz, CD₃OD, ppm): δ 8.31 (s, 1H), 7.37 (d, J=3.6 Hz, 1H),6.68 (d, J=3.6 Hz, 1H), 6.62 (t, J=6.4 Hz, 1H), 4.69 (t, J=7.0 Hz, 1H),3.80 (dd, J=12.0 Hz, J=30.0 Hz, 2H), 3.09 (s, 1H), 2.67-2.54 (m, 2H).LC-MS: (ES, m/z): 276.00 [M+H]⁺.

Compound 11A:7-((2R,4S,5R)-5-ethynyl-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-yl)pyrrolo[2,1-f][1,2,4]triazin-4(3H)-one

¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 10.25 (brs, 1H), 7.86 (s, 1H), 6.83(d, J=4.5 Hz, 1H), 6.63 (d, J=4.2 Hz, 1H), 5.53 (t, J=7.5 Hz, 1H),5.31-5.25 (m, 1H), 5.09-5.05 (m, 1H), 4.31-4.27 (m, 1H), 3.55-3.45 (m,2H), 3.33 (s, 1H), 2.35-2.18 (m, 2H). LC-MS: (ES, m/z): 298.00 [M+Na]⁺.

Compound 22A:7-((2R,4S,5R)-5-ethynyl-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-yl)imidazo[2,1-f][1,2,4]triazin-4(3H)-one

¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.12 (s, 1H), 7.56 (s, 1H), 5.45 (t,J=7.4 Hz, 1H), 5.35 (d, J=4.0 Hz, 1H), 5.06 (brs, 1H), 4.33 (brs, 1H),3.56-3.46 (m, 2H), 3.32 (s, 1H), 2.42-2.33 (m, 1H), 2.28-2.22 (m, 1H).LC-MS: (ES, m/z): 277.10 [M+H]⁺.

Compound 23A:8-((2R,4S,5R)-5-ethynyl-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-yl)pyrazolo[1,5-a][1,3,5]triazin-4(3H)-one

¹H-NMR: (400 MHz, d₆-DMSO, ppm): δ 8.08 (s, 1H), 7.98 (s, 1H), 5.30 (t,J=7.4 Hz, 1H), 5.25 (d, J=5.2 Hz, 1H), 5.24-5.11 (m, 1H), 4.32 (q, J=5.2Hz, 1H), 3.53 (dd, J=11.6 Hz, J₂=32.0 Hz, 2H), 3.36 (s, 1H), 2.36-2.29(m, 1H), 2.16-2.10 (m, 1H). LC-MS: (ES, m/z): 274.80 [M−H]⁻.

TABLE 5 Structure (Substrate) Inosine Product T_(1/2) Deoxy- adenosine

<10 min EDA

<60 min Example Inosine No. Structure (Substrate) No. Inosine ProductT_(1/2) 1

1A

12 days 2

2A

16 h 4

4A

NA 8

8A

NA 9

9A

NA 11

11A 

3 h 22

22A 

10 min 23

23A 

10 min

While the foregoing specification teaches the principles of the presentinvention, with examples provided for the purpose of illustration, thepractice of the invention encompasses all of the usual variations,adaptations and/or modifications that come within the scope of thefollowing claims. Recitation or depiction of a specific compound in theclaims (i.e., a species) without a specific stereoconfigurationdesignation, or with such a designation for less than all chiralcenters, is intended to encompass the racemate, racemic mixtures, eachindividual enantiomer, a diastereoisomeric mixture and each individualdiastereomer of the compound where such forms are possible due to thepresence of one or more asymmetric centers. All publications, patentsand patent applications cited herein are incorporated by reference intheir entirety into the disclosure.

1-65. (canceled)
 66. A pharmaceutical composition comprising aneffective amount of a compound that is: 1)(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;2)(2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;3)(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;4)(2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;5)(2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;6)(2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;7)(2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;8)(2R,3S,5R)-5-(2,4-diamino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;9)(2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;10)(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-hydroxy-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile;11)(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;12)(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-hydroxy-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile;13)((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 14)((2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 15)((2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 16)((2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 17)((2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 18)((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-cyano-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 19)((2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 20)((2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 21)((2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 22) (2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;or 23)(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;or a pharmaceutically acceptable salt thereof, and an effective amountof one or more HIV antiviral agent selected from: abacavir, abacavirsulfate, abacavir+lamivudine, abacavir+lamivudine+zidovudine,amprenavir, atazanavir, atazanavir sulfate, AZT, capravirine, darunavir,dideoxycytidine, dideoxyinosine, delavirdine, delavirdine mesylate,dolutegravir, doravirine, efavirenz, efavirenz+emtricitabine+tenofovirdisoproxil fumarate, 4′-ethynyl-2-fluoro-2′-deoxyadenosine,elvitegravir, emtricitabine, emvirine, enfuvirtide, etravirine,fosamprenavir calcium, indinavir, indinavir sulfate, lamivudine,lamivudine+zidovudine, lopinavir, lopinavir+ritonavir, maraviroc,nelfinavir, nelfinavir mesylate, nevirapine, PPL-100, raltegravir,rilpivirine, ritonavir, saquinavir, saquinavir mesylate, stavudine,tipranavir or vicriviroc, and a pharmaceutically acceptable carrier. 67.A method for the treatment of infection by HIV or for the treatment ordelay in the onset of AIDS in a human subject in need thereof whichcomprises administering to the subject an effective amount of a compoundthat is: 1)(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;2)(2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;3)(2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;4)(2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;5)(2R,3S,5R)-5-(4-amino-5-bromo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;6)(2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;7)(2R,3S,5R)-5-(4-amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;8)(2R,3S,5R)-5-(2,4-diamino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;9)(2R,3S,5R)-5-(4-amino-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;10)(2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-3-hydroxy-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile;11)(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;12)(2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-3-hydroxy-2-(hydroxymethyl)tetrahydrofuran-2-carbonitrile;13)((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 14)((2R,3S,5R)-5-(4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 15)((2R,3S,5R)-5-(4-amino-5-methyl-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 16)((2R,3S,5R)-5-(4-amino-2-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 17)((2R,3S,5R)-5-(4-amino-5-chloro-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 18)((2R,3S,5R)-5-(4-amino-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-2-cyano-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 19)((2R,3S,5R)-5-(4-aminopyrrolo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 20)((2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 21)((2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-3-hydroxytetrahydrofuran-2-yl)methyltetrahydrogen triphosphate; 22) (2R,3S,5R)-5-(4-aminoimidazo[2,1-f][1,2,4]triazin-7-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;or 23)(2R,3S,5R)-5-(4-aminopyrazolo[1,5-a][1,3,5]triazin-8-yl)-2-ethynyl-2-(hydroxymethyl)tetrahydrofuran-3-ol;or a pharmaceutically acceptable salt thereof, and an effective amountof one or more HIV antiviral agent selected from: abacavir, abacavirsulfate, abacavir+lamivudine, abacavir+lamivudine+zidovudine,amprenavir, atazanavir, atazanavir sulfate, AZT, capravirine, darunavir,dideoxycytidine, dideoxyinosine, delavirdine, delavirdine mesylate,dolutegravir, doravirine, efavirenz, efavirenz+emtricitabine+tenofovirdisoproxil fumarate, 4′-ethynyl-2-fluoro-2′-deoxyadenosine,elvitegravir, emtricitabine, emvirine, enfuvirtide, etravirine,fosamprenavir calcium, indinavir, indinavir sulfate, lamivudine,lamivudine+zidovudine, lopinavir, lopinavir+ritonavir, maraviroc,nelfinavir, nelfinavir mesylate, nevirapine, PPL-100, raltegravir,rilpivirine, ritonavir, saquinavir, saquinavir mesylate, stavudine,tipranavir or vicriviroc.
 68. A pharmaceutical composition comprising aneffective amount of a compound that is:

or a compound that is a pharmaceutically acceptable salt thereof, and aneffective amount of one or more HIV antiviral agent selected from:abacavir, abacavir sulfate, abacavir+lamivudine,abacavir+lamivudine+zidovudine, amprenavir, atazanavir, atazanavirsulfate, AZT, capravirine, darunavir, dideoxycytidine, dideoxyinosine,delavirdine, delavirdine mesylate, dolutegravir, doravirine, efavirenz,efavirenz+emtricitabine+tenofovir disoproxil fumarate,4′-ethynyl-2-fluoro-2′-deoxyadenosine, elvitegravir, emtricitabine,emvirine, enfuvirtide, etravirine, fosamprenavir calcium, indinavir,indinavir sulfate, lamivudine, lamivudine+zidovudine, lopinavir,lopinavir+ritonavir, maraviroc, nelfinavir, nelfinavir mesylate,nevirapine, PPL-100, raltegravir, rilpivirine, ritonavir, saquinavir,saquinavir mesylate, stavudine, tipranavir or vicriviroc, and apharmaceutically acceptable carrier.
 69. The pharmaceutical compositionof claim 68 wherein the compound is


70. The pharmaceutical composition of claim 68 wherein the compound is apharmaceutically acceptable salt of


71. A method for the treatment of infection by HIV or for the treatmentor delay in the onset of AIDS in a human subject in need thereof whichcomprises administering to the subject an effective amount of a compoundthat is

or a compound that is a pharmaceutically acceptable salt thereof, and aneffective amount of one or more HIV antiviral agent selected from:abacavir, abacavir sulfate, abacavir+lamivudine,abacavir+lamivudine+zidovudine, amprenavir, atazanavir, atazanavirsulfate, AZT, capravirine, darunavir, dideoxycytidine, dideoxyinosine,delavirdine, delavirdine mesylate, dolutegravir, doravirine, efavirenz,efavirenz+emtricitabine+tenofovir disoproxil fumarate,4′-ethynyl-2-fluoro-2′-deoxyadenosine, elvitegravir, emtricitabine,emvirine, enfuvirtide, etravirine, fosamprenavir calcium, indinavir,indinavir sulfate, lamivudine, lamivudine+zidovudine, lopinavir,lopinavir+ritonavir, maraviroc, nelfinavir, nelfinavir mesylate,nevirapine, PPL-100, raltegravir, rilpivirine, ritonavir, saquinavir,saquinavir mesylate, stavudine, tipranavir or vicriviroc.
 72. The methodof claim 71 wherein the compound is


73. The method of claim 71 wherein the compound is a pharmaceuticallyacceptable salt of